Not to take anything away from Dave but sometimes I lurk on the Modern Blues Harmonica forum that Adam Gussow supports. Today I checked out the rest of the site and found some jam tracks for sell. The two volumes cost a whopping total of $20.00. They're great. I would highly recommend them. Also the Grove Trax that Jimi Lee has produced are outstanding and I think you can get those through Dave. I think supporting these efforts is giving back to the community that David has suggested. If you have any other jam tracks other than David's post it here for everyone to see.
By the way... Let's not lurk on these forums... be contributors. I've determined that I'm going to post here and on the MBH forum more often.
5731 Meridian Ave.
San Jose, CA 95118
Hey Jon, good on you. Mr Shoji at shoblues.Com has some useful tracks available too. They are all quite amusingly named. It's generally pretty easy to tell what song we have. They are nice for playing particular songs which have non- standard structures. Just you're fool comes to mind, with it's 8 bar verses and alternate 8 bar bridge an 12 bar instrumentals. I ain't got you is another number with that structure, but I'm not sure if shoji has made a track for that. A bunch of little Walter tunes there though. They're not very expensive.
Also I just remembered that Dennis Gruenling sells tracks. From memory, Dennis makes things available in lots of different keys. I haven't bought any, so can't really comment further.