The EndNote Styles collection contains more than 3000 bibliographic styles for a variety of disciplines. You can download files individually below or as a complete set for version 8 and up.

NOTE: rename any files you have customized as the new versions will overwrite existing files. Once the Zip file(s) is downloaded to your desktop, copy the file(s) to the appropriate folder in your EndNote program directory (usually located in Windows—C:\Program Files\EndNote\Styles or Mac OS X—Harddrive:Applications:EndNote:Styles).
VERSION 4-7: Download an archive of styles updated through April 2006.

You can also download files individually via FTP: Mac / Windows. If you can't find the style you are looking for you can suggest a new style, as well as updates to an existing style.