just go with the 50mm f1.8. A flickr contact of mine has one of those and takes awesome portraits with it.
http://www.flickr.com/photos/micahheatwole/
Cant beat the price either. But the f1.4 is somewhat better but you pay for it. The best is that f1.2 but you really pay for that.
i would say get that f1.8 for now and save up for a 70-200 f2.8. Canon version is nice and so is the sigma APO version. I love my sigma. Real quality glass.