Go to harmonicalinks.com, click on "MIDI". Second from the top, left hand side. That takes you to a page of links. Country, Blues, Jazz... Looks like hundreds of songs.
A quick google search will turn up tons of music-only jam tracks on the web. You can get some right here in Jon's Jamming Room on the main site. Harmonicalessons.com also has some, and there's another site (blues tracks or something like that) that also has generic backing tracks in the most common keys and at many different tempos. I've found having a few of these on the computer or mp3 player come in handy for practicing.
I am so in need of practice, but there are no musicians living around here :) In fact, I have never seen or met anyone playing harmonica yet, no human interaction what so ever. Thanks to internet I can pretty much follow up tough...
Under these circumstances, the best way to practice is playing something in the background and trying to go with the flow. I just record myself, listen to it later and realize how much I suck! But it will happen one day!
My question is, could you recommend some -harmonica free- good songs to play on (if this is the correct word??) For example, I realized that BB's 'Blues on the bayou' is just great for that as there are a lot of solos and NO harmonica. Great for practice. But when I try practicing with Charlie Musselwhite's albums, I leave the harmonica aside for a month, or eat it at the end. I hate that guy! Does he really have to be that good? You get my point, I guess...