Two thoughts:

1)Akai "Riff-o-Matic" ....slows down 13 and 26 second passages (the difference being 32 and 16 bit sampling, respectively) to 1/3, 1/2, or 2/3 the original speed without changing pitch. There are functions to adjust the pitch as well, to match the tuning of your instrument. Here's one on ebay that explains all the features. Not a bad price either, if $40.00 is the winning bid.

2)Tascam CD-GT1 Trainer. Here's one here that explains the functions. Only does CD's though. The best thing about this machine is you're not limited on the length of the loop; you can sample any phrase regardless of length. You also have more speed options: 50%; 66%; 84%; 92% of original speed.