I posted exactly the same thread a while back when I was looking for a decent 50mm.I've used a 50mm 1.5 Nokton which someone here lent me, which was a superb lens ( though quite large ) and I ended up buying a Canon 50mm 1.8 which I absolutely love and use all the time. I've also heard excellent things about the Canon 1.4 and 1.2.You do need to decide on your budget, the widest aperture you really want to use and the general signature and feel of the lens too.I'll buy myself an old uncoated Elmar or somesuch when I have the spare cash simply for a different 'feel' when I need it.Others will come in and say you really should get Leica glass...unfortunately I don't know first hand just how good it is yet but if you can afford it then you should certainly think about it.