Anyone got or know of a good blues back track?

I've been searching for a bit but can't find a good blues back track (any key) to use while just messing around.
Hoping someone in here has already done some heavy keyboard lifting and would share the fruits of their labor with me.
So if anyone has a back track in any key that has some good length to it I would greatly appreciate it.

 

I'm assuming you play guitar, right? http://www.guitarbackingtrack.com/ has some pretty good backing tracks -- and some not so good, it's kind of hit and miss. I'm not sure if hey have a generic blues track, but they have some Clapton, Hendrix, Zeppelin, etc.

 

Guitar Center sells "Band in a Pocket" CDs with multiple tracks. All pretty vanilla, but you can add all the toppings you want.