A good vintage beginner picture camera, preferably an SLR. Any thoughts? brands? sites?

Pentax K1000 is THE workhorse students' camera and I guess it qualifies as vintage. Look into a Spotmatic, also, which is a bit upscale from the K1000, but a fine camera. A somewhat newer Pentax that still works well in manual modes is the P30 and newer versions of the P30. You just set the stuff directly without using plus or minus EV settings. I bought one about 10-15 years ago when my Spotmatic broke.

Shop at B&H Photo, eBay, Keh.com, Adorama...

I think starting with film would help you think more throughly before each shot, where as digital you can snap away to infinity. Sure it would be require more from you, but i think it'd be much more rewarding. I wish I had started with film! still havent.

If you decide to go with digital, I can say that the Nikon d40 is a great entry level, decent kit lens/price. It only auto focuses on AF-S lens (which get kinda expensive), but you can mount all sorts of vintage glass on the d40 (no metering/auto focus).

If what you're looking for is a film camera your choices are unlimited.

A canon t50 is "idiotproof" and cheap.
Nikon f2's are pro level cameras.
Olympus om1's and om2's are excellent cameras.

You'd be wise not to bother with a film camera at all however. Film is quickly nearing the end of its days. Within 5 years even medium format film will disappear and its unlikely 35mm film will even be made by then. You'd be far better off with the cheapest digital slr you can find. there are last gen canons, olys and maybe nikons on ebay for a stunning price. Be warned however that if you go slr the expense is in the Lenses (and the endless amount of accessories) not in the body. Get the best body you can afford then expect to spend from 100 to 5000 per lens from then on.