Good advice from Brad, but I'd pick a body that supports currently available lenses, at least partially.
Agreed, but you can usually find a K-1000 and a lens on ebay for under a c-note. Good for learning, and makes a dandy backup or B&W setup. Plus, it's always good to go back to for a little brushup on the skills. I still have my original K-1000 with the Pentax 52mm lens on it. It's usually loaded with 400 speed Tri-X for candid B&W work.
My everyday rig is a Canon Elan with a Canon 24-70 F/2.8L hung on the front, an auxiliary battery pack/grip, and a Speedilite 380 flash. At only 2 fps the drive is a little slower than I'd like, but works fine for my needs, and the body has more functions than I'll ever use. When I got the body I bought a Tamron 28-80 for it but was never satisfied with the pics. This L-series Canon, however, exceede my wildest expectations (as it should have, for what the darn thing cost!). The only problem is that the thing is so gosh-awful heavy.
Brad