Among the most useful Spotlight features the calculator is top-ranked, at least for me. It comes up in a fraction of a second, and I'm ready to do whatever has to be done (calculated). And, sometimes, it's more complicated than 2+5. In any case, you can use it as a backup, confirming any results of mental number juggling.
In addition, many users know that Boolean operators like "AND", "OR" and "NOT" may be used to combine search terms. Caveat: Uppercase is essential!
| kMDItemAcquisitionMake | Make of the device used to acquire this document | make |
| kMDItemAcquisitionModel | Model of the device used to acquire this document | model |
| kMDItemAlbum | Title for a collection of media, such as a record album | album,title |
| kMDItemAltitude | The altitude of the item in meters above sea level, expressed using the WGS84 datum. Negative values lie below sea level. | altitude |
| kMDItemAperture | Size of the lens aperture as a log-scale APEX value | aperture,fstop |
| kMDItemAppStoreCategory | App Store Category item is a member of | category |
| kMDItemApplicationCategories | Categories application is a member of | categories |
| kMDItemAudiences | Who the document is intended for | to,audience |
| kMDItemAudioChannelCount | Number of channels in the file's audio data | channels |
| kMDItemAudioTrackNumber | Track number of the song that is part of an album | tracknumber |
| kMDItemAuthorAddresses | Addresses for authors of this item | from |
| kMDItemAuthorEmailAddresses | Email addresses for authors of this item | from,email,mail |
| kMDItemAuthors | Authors of this item | from,author,with,by |
| kMDItemBitsPerSample | Number of bits per sample | bitspersample,bps |
| kMDItemCity | City of the item | city |
| kMDItemCodecs | Codecs used to encode and decode the media | codec |
| kMDItemColorSpace | Color space model of this image | colorspace |
| kMDItemComment | Comments about this item | comment |
| kMDItemComposer | Composer of the song in the audio file | by,composer,author |
| kMDItemContactKeywords | Contacts associated with this item | contact,contactkeyword,keyword |
| kMDItemContentCreationDate | Date when the content of this item was created | contentcreated,created,date |
| kMDItemContentModificationDate | Date when the content of this item was modified | contentmodified,modified,date |
| kMDItemContributors | People or organizations contributing to the content of the document | by,contributor,author,with |
| kMDItemCopyright | Copyright information about this item | copyright |
| kMDItemCountry | Country or location where the item was created according to the provider | country |
| kMDItemCoverage | Extent or scope of the content of the document | coverage |
| kMDItemCreator | Application used to create the document | creator |
| kMDItemDateAdded | Date when this item was last moved | dateadded,added,date |
| kMDItemDeliveryType | Method used to deliver the media (Fast Start or RTSP) | delivery |
| kMDItemDescription | Description of the content of the document | description,comment |
| kMDItemDisplayName | Localized name of the file | name,displayname |
| kMDItemDocumentContainer | Containing folder of item | container |
| kMDItemDueDate | Date this item is due | duedate,date |
| kMDItemDurationSeconds | Duration of this item in seconds | duration,time |
| kMDItemEXIFVersion | Version of EXIF used to generate the metadata | exifversion |
| kMDItemEditors | Editors of this item | editor |
| kMDItemEmailAddresses | Email addresses associated with this item | email,mail |
| kMDItemExecutableArchitectures | Architectures the item requires to execute | architectures |
| kMDItemExecutablePlatform | Platform the item requires to execute | platform |
| kMDItemExposureMode | Mode used for the exposure | exposuremode |
| kMDItemExposureProgram | Type of program used by the camera to set the exposure: Manual, Normal, Aperture priority, ... | exposure,exposureprogram |
| kMDItemExposureTimeSeconds | Time the lens was open during exposure | exposuretime,time |
| kMDItemExposureTimeString | Exposure time | exposuretime,time |
| kMDItemFNumber | Focal length of the lens divided by the diameter of the aperture | fnumber,fstop |
| kMDItemFSContentChangeDate | Date the file content was last changed | modified |
| kMDItemFSCreationDate | Date the file was created | created |
| kMDItemFSInvisible | Whether the file is visible | invisible |
| kMDItemFSIsStationery | Whether the file is stationery | stationery |
| kMDItemFSName | Name of the file | filename |
| kMDItemFSOwnerGroupID | Group ID of owner of the file | group |
| kMDItemFSOwnerUserID | User ID of the owner of the file | owner |
| kMDItemFSSize | Logical size of the file on disk in bytes | size |
| kMDItemFinderComment | Spotlight comment for this item | comment,spotlightcomment |
| kMDItemFlashOnOff | Whether the picture was taken using a flash | flash |
| kMDItemFocalLength | Focal length of the lens in millimeters (mm) | focallength |
| kMDItemFonts | Fonts used in this item | font |
| kMDItemHasAlphaChannel | Whether the image has an Alpha channel | alpha |
| kMDItemHeadline | Publishable summary of the contents of the item | headline,title |
| kMDItemISOSpeed | ISO speed of the camera when the picture was taken | iso |
| kMDItemIdentifier | Reference to a resource within a given context | id |
| kMDItemInstantMessageAddresses | Instant message addresses associated with this item | chat,imname |
| kMDItemInstructions | Other information concerning the item, such as handling instructions | instructions |
| kMDItemIsApplicationManaged | The file is owned and managed by an application | appmanaged |
| kMDItemIsGeneralMIDISequence | Whether the MIDI sequence contained in the file is setup for use with a General MIDI device | ismidi |
| kMDItemIsLikelyJunk | Whether the file is likely to be considered a junk file | isjunk |
| kMDItemKeySignature | Musical key of the song in the audio file | key,keysignature |
| kMDItemKeywords | Keywords associated with this item | keyword |
| kMDItemKind | Kind of this item | kind |
| kMDItemLanguages | Languages of the content of the document | language |
| kMDItemLastUsedDate | Date when this item was last used | lastused,date |
| kMDItemLatitude | The latitude of the item in degrees north of the equator, expressed using the WGS84 datum. Negative values lie south of the equator. | latitude |
| kMDItemLayerNames | Names of the layers in the file | layer |
| kMDItemLongitude | The longitude of the item in degrees east of the prime meridian, expressed using the WGS84 datum. Negative values lie west of the prime meridian. | longitude |
| kMDItemLyricist | Lyricist of the song in the audio file | by,lyricist,author |
| kMDItemMaxAperture | Smallest F number of the lens in APEX value units, usually in the range of 00.00 to 99.99 | maxaperture |
| kMDItemMediaTypes | Media types present in the content | media,contains,mediatype |
| kMDItemMeteringMode | The metering mode (Unknown, Average, CenterWeightedAverage, Spot, MultiSpot, Pattern, Partial) | metering,meteringmode |
| kMDItemMusicalGenre | Musical genre of the song in the audio file | genre,musicalgenre |
| kMDItemMusicalInstrumentCategory | Instrument category to which the file belongs | instrument,instrumentcategory |
| kMDItemMusicalInstrumentName | Name of instrument relative to the instrument category | instrument,instrumentname |
| kMDItemNamedLocation | Name of the location or point of interest | location |
| kMDItemNumberOfPages | Number of pages in the document | pages |
| kMDItemOrganizations | Organizations that created the document | organization |
| kMDItemOrientation | Orientation of the picture (landscape or portrait) | orientation |
| kMDItemPageHeight | Height of the document page in points | pageheight,height |
| kMDItemPageWidth | Width of the document page in points | pagewidth,width |
| kMDItemPath | Complete pathname of this file | path |
| kMDItemPhoneNumbers | Phone numbers associated with this item | phone,phonenumber |
| kMDItemPixelCount | Total number of pixels in the document | pixelcount |
| kMDItemPixelHeight | Height of the document in pixels | pixelheight,height |
| kMDItemPixelWidth | Width of the document in pixels | pixelwidth,width |
| kMDItemProducer | Producer of this item | producer |
| kMDItemProfileName | Name of the color profile used for the image | profile |
| kMDItemPublishers | Publisher of the document | publisher |
| kMDItemPurchaseDate | Date this item was purchased | purchasedate |
| kMDItemRecipientAddresses | Addresses for recipients of this item | to |
| kMDItemRecipientEmailAddresses | Email addresses for recipients of this item | to,email,mail |
| kMDItemRecipients | Recipients of this item | to,recipient,with |
| kMDItemRecordingDate | Date the song was recorded | recordingdate,date |
| kMDItemRecordingYear | Year the item was recorded | yearrecorded,year |
| kMDItemRedEyeOnOff | Whether 'red eye' correction was on or off | redeye |
| kMDItemResolutionHeightDPI | Resolution height of this image in DPI | heightdpi,dpi |
| kMDItemResolutionWidthDPI | Resolution width of this image in DPI | widthdpi,dpi |
| kMDItemRights | Link to information about the rights held on the document | rights |
| kMDItemSecurityMethod | Encryption method used to make the document secure | security,securitymethod |
| kMDItemStarRating | User Rating | starrating |
| kMDItemStateOrProvince | State or province of the item according to the provider | state,province |
| kMDItemStreamable | Whether the content is prepared for streaming | streamable |
| kMDItemSubject | Subject of this item | subject,title |
| kMDItemTempo | Tempo of the music in the audio file in Beats Per Minute | tempo |
| kMDItemTextContent | Text content of this item | content,contains,intext |
| kMDItemTheme | Theme of this item | theme |
| kMDItemTitle | Title of this item | title |
| kMDItemTotalBitRate | Combined bit rate of the audio and video in the media | totalbitrate,bitrate |
| kMDItemURL | URL of this item | url |
| kMDItemUsedDates | Dates when this item was used | used,date |
| kMDItemUserTags | Tags associated with this item | tag |
| kMDItemVersion | Version number of this item | version |
| kMDItemVideoBitRate | Bit rate of the video in the media | videobitrate,bitrate |
| kMDItemWhereFroms | Where the item came from | from,source,wherefrom |
| kMDItemWhiteBalance | White balance setting of the camera when the picture was taken | whitebalance |
Remember that a keyword always requires a colon (:) and an argument. 1 usually stands for "true" and 0 for "false", as in "flash:1" (finding all images made with a flash turned on).
Also, for international users, the keywords differ substantially. As soon as I find the time, I will publish counterparts for other languages. (MacConfig)
