Don't forget that Pentax is still producing the FA 50mm f1.4, you can buy it as new.
Originally posted by manntax Best AF - SMC-F 50mm f1.7 , best MF M42=Super Takumar 50mm f1.4 8-element, K-mount= SMC-A 50mm 1.4 ooooorr - not for faint hearted , SMC-A 50mm f1.2 ( which I am actually approaching :P )
This is a quite good list. Just add the DA* 55mm f1.4 in there.
One thing to keep in mind is that MF with f1.4 lenses is difficult - modern DSLRs are not really made for that. DA 50mm f1.8 can be found very affordable these days, especially used. It is the same design as FA 50mm f1.7, F 50mm f1.7, A 50mm f1.7 and M 50mm f1.7, if I remember correctly. This is a lineage, with optical differences between the lenses mostly stemming from coatings, aperture shape, and precision of machining. There are other differences, for example the M 50mm is metal, while the DA is plastic. Anyway, just buy one of them, you can always resell at a minimum loss if it is disappointing.