James Creasey - Music For Science And Space -http://creaseyproductions.com
Mark Petersen - Loch Ness Productions - http://www.lochnessproductions.com
See MUSIC BACK-PACK Library pages, where there are samples of every track from all volumes. See also http://www.geodesium.com where there are samples of every track from all eight Geodesium albums, and an occasional full-length track as well.
Stock 20 (www.Stock20.com) all different kinds of instrumental music in a wide variety of lengths for crossfadeability.
Adobe Soundbooth (part of Creative Suite)
Footage Firm (www.footagefirm.com) sells packs of music with multiple versions of each track—optional endings, stingers, .... Also collections of sound effects. Don't pay full price—items are frequently placed "on sale" for "free" (pay shipping). If you start an order and don't complete the sale, you may get an automatic email with a code that will give you 25% off if you complete the sale.