Pentax SMC-M, Minolta MD Rokkor, Canon FD, Olympus M Zuiko, Fujica, are all good bets for nice Bokeh. Anything faster than F/2 is best. The f/1.7, f/1.8, and f/1.4 lenses are all good options. The f/1.7 and 1.8 lenses can usually be found for between $40 and $70 or so. Try KEH. You will pay even less at thrift shops, and maybe get a free camera with the lens. Helios might be OK, but might not be to your taste either. The Russians generally have different Bokeh. There are all sorts of affordable lenses in M-42 (Pentax Screw) mount as well, such as the Takumars mentioned above. I have a Minolta MC Rokkor 58mm/1.4 that is very nice (and was cheap), but I actually think the blur is nicer on some of the f/1.8 or f/1.7 lenses. The newer MD Rokkor lenses have better coatings. Whether you prefer the old-fashioned lenses with less or no coatings to the newer lenses with better coatings is a matter of personal preference. Pentax SMC-M 50mm f/1.4 is looks really nice, but I only have the SMC-M 50mm/1.7 and it is fine. I think Minolta MD Rokkor lenses are especially good on digital cameras, and they tend to be cheap. Canon FD 50mm f/1.8 lenses have a more modern look, but are also very nice, and inexpensive.