I am in love with my 50 1.8. I have made a lot of keepers with it as well. Tack sharp, pretty good AF speed too. Like stated above, the build quality is pretty bad, but I haven't had any problems with it. I also have the 85 1.8 which is also awesome for a short tele, and the 1.8 reqally blurs out the background well. I also have the 17-40 f4 L. I believe it is nearly as sharp as the others, but has light fall off on the corners at 17mm. It works for a lot of shots, but sometimes can ruin a shot.

It's hard to suggest a lens without knowing what you are shooting.