I recorded a groovy backing track to practice improv soloing over. This is a really fun way to practice. Pick a key, write a simple groove, then improv over it while recording it on video. You can watch and listen back to critique yourself.
Yes you can go on youtube and find a million pre-recorded backing tracks, but that takes away the fun of writing a groove that you think might be challenging to play to. http://youtu.be/mZGe77dct5k