If you're looking for an approach to loop manipulation other than those found here, check out the sample libraries from Ilio Entertainments (www.ilio.com) and Spectrasonics that employ Groove Control. Groove Control is similar to what you get when working with ReCycle, but the loop slicing has already been done for you. That means you just load a Groove Control — enabled loop into your sampler, open the Groove MIDI tracks in your sequencer, and get down to business.
I'd been working with the audio version of Ilio's Ethno Techno sample library, painstakingly ripping all the files to my PC, cutting the tracks into individual hits, and jumping through a number of hoops to tempo-match various samples. Although I've occasionally used Acid to do some of the tempo-matching for me, the number of steps involved often outweigh the benefits. With the Groove Control version of the CD-ROM, I dumped the sample files into my Kurzweil K2500, assigned each patch to the proper MIDI channel, and loaded the associated Standard MIDI Files into my sequencer. Within a few minutes, all of the features of my sequencer — tempo shifting, quantizing, Velocity scaling, and more — became available to manipulate the sounds. And I never once cracked the manual!
Keep in mind that there is one major limitation with Groove Control: it works only with loops from Ilio and Spectrasonics. There are nine Groove Control — activated titles (starting at $199), covering a broad range of categories. Each CD-ROM packs hundreds of megabytes of samples, and new loop CDs are coming on the market all the time.