Icompetech.com has a large collection of free audio files for downloading. The music and loops are provided royalty-free and are suitable for use in film making, theatre productions, podcasting, and composition/re-mixing.
Several categories are provided for musical styles including Acid Jazz, Bach, Beethoven, Disco, Experimental, Latin, Orchestral, Polka, Rap/RnB, Reggae, Rock/Pop, Space Opera, Demo/Other. Compositions are supplied in mp3 format and vary in duration from seconds to several minutes.
Here’s an example from the Experimental category. Title: Intuit Length: 7 minutes 50 seconds.
Zipped loop packs can be downloaded directly from the site or via p2p networks Shareaza, Limewire, Xolox, or other Magnet-enabled P2P applications. The loop packs on the site change every month. There are packs for instruments and vocals with the size of each pack ranging from around 10 Megs to 200 Megs.