I think the 40mm 2.8 is a good lens, it may not be as great in low light, but you get crazy sharpness with it, also perfect for walk around. I currently have the 10-22, 24-105 and picking up the 40mm just for that gap. It can even be used for full body portrait shots as well, the 1.8 is great as well though, bokeh and awesome in low light. Im not a fan of the Canon 1.4, I just dont think its night and day as some people say, guess it depends on what your shooting. For that money I'd rather buy a Tamron 17-50 2.8 VC II.
In reference to my night/day scenario. The 1.8ii missed focus as much as it hit it seemed, not to mention it was slower and it very loud. When you did hit focus it could produce great images, I just got tired of fighting with it. $100 vs the $225 I gave for a 1.4, the 1.4 was night/day for the small price bump.







