I dunno if I can say this here but I go to the lespaulforum.com where they have a JamZone section. It is a pretty lively section where they accept anyone to participate, even if you don't have a Les Paul guitar (I don't)
You get a huge selection of backing tracks, all copyright free (most of the time anyways), and of various quality of course.
The fun part is you can upload your take on whatever backing and read the comments from the other players and listen to what the others did and comment yourself.
Multitude of takes on the same backing, it's amazing they're all different.
It's a great learning tool.