I have written in Playing With Sound, and blogged recently, about improvisation. I thought it might be useful, in addition to the chord charts, to upload some midi files so you can improvise along in the keys of C, F and G. There's no mystery. Provided you can play the major scale of the appropriate key you can't go wrong. So C major goes with '12 Bar in C' and so on.
The files will play in Windows Media Player, RealPlayer and QuickTime. All you need to do is click on the link. If you want to save them to your computer, click on File (top left of your screen) and then 'Save Page As'. Decide where you want to put them and click OK. I went to the trouble of creating them in three different styles, each cheesier than the one before.
12 Bar in C
12 Bar in F
12 Bar in G
I'll take this further in a future post.