Looptastic Producer 1.1 (iTunes App Store)

...is a $4.99 (introductory price) iPhone app that lets you remix and perform music using loops. The feature that sets this Producer version apart from the Electro ($4.99) and Electro Lite (free) editions is the ability to import your own loops from a Windows, Mac OS X, or Linux PC. It does this by providing its own web server on an iPhone or iPod touch setup on port 8080 (a common port to use for alternative web browsers on servers). You can't save your mix in this version. But, its creator notes this feature is coming to a future release.

Soundtrends Looptastic product site

One issue I ran into the first time I tried it on my iPod touch was a low memory warning. I imagine that the need to work with multiple audio loops/files simultaneously is quite a memory hog. Fortunately, a simple soft reset of my iPod touch resolved the issue.