Sound Loops

Many sound studios sell sets of music rather than just single tracks.
Many of the "free" loops on these sites are only free for personal use. Some require you to purchase a license before using them commercially.
Licensed and free tracks generally allow you to use them in any manner you wish except for posting, reselling, or re-distributing them.
Posting licensed tracks to a company server generally requires a multi-user license.

Website	Qty	Search	Categorized	Type
Digital Vision		N	Y	Pay
FlashKit - Largest library we know of.	5000+	Y	Y	Both
FotoSearch - FotoSearch resells sounds from several vendors.	Lots	N	Y	Pay
FreePlay Music - Check out this collection of some of the highest quality sound loops on the market. Some loops can be used for personal use.	800+	Y	Y	Pay
GraphicsScene - CD Compilations only. No individual downloads.	5 Sets	N	Y	Pay
Killersound - Downloadable and CD Sets of High Quality Sound Effects	Lots	N	Y	Pay
Killertracks - A division of BMG. Provides High Quality Sound Effect sets.	Lots	N	Y	Pay
Luppaerolla - Italian sound loop library. Some nice stuff, but reading Italian would really help.	50+	N	Y	Free
Live Motion Central	20+	N	Y	Free
Matton: Music - Provider of Royalty Free Music Clips, Royalty Free Songs and Royalty Free Sounds. All available for immediate purchase and download.	500+	N	Y	Pay
NeoSounds - These guys sell a limited number of sound fx and music on CD. However, at $69 per CD, the price is decent.	500+	N	N	N
Sounddogs.com - Large library of individually downloadable sound effects.	Lots	Y	Y	Pay
Web Builder	15+	N	N	Share
Google loop directory - list of loop sites	n/a	n/a	n/a	n/a