I've been looking to get a 50mm f1.4 lens and was initially looking at the Canon, and then later started looking at the Sigma as I liked the bokeh more in comparison photos.
After reading a number of reviews and forums, the consensus seems to be that both lenses are great when they work, but "don't buy the Sigma 'cause you may get one with front- or back-focussing issues" and "don't buy the Canon because it's very soft wide open, and has a fragile focus mechanism that can easily break".
So my question is: Are these people being overly critical, or are these valid concerns? If so, I might have to start looking at a different focal length for my portrait lens =/
Everything has been pretty much said in this thread. But if you don't mind manual focusing, I recommend the superb Asahi Pentax S-M-C Super-takumar 50mm f1.4. With any luck, you can find them on a good price, and I would dare to say they beat the Canon f1.4 and Sigma f1.4 in overall image quality (bokeh, contrast, colors). And since you have a crop body, there shouldn't be any problems with mirror. However, if you someday update to full frame, then there might be problems with the lens hitting the mirror...