Pentax K1000 (cheap, good quality, and plentiful lenses) or Nikon FG or FM / FM2 (superb glass, well built). Avoid Canon manual focus, as investing in FD mount lenses is a bit folly if you decide you want a more modern camera as well as a mechanical one (though plenty of people use and love theirs), the bodies sometimes develop shutter issues...

Avoid Digital too (Especially Canon digital) it's really boring.