psycho bob said:Only a fool wouldn't consider Sigma and Tamron lenses. I personally use a Sigma SD9 with various lenses and still use film SLR's and rangefinder cameras. Sigma's EX lenses are equally as good and often better then their Canon counterparts. At the price range you will be looking at a lense from any of the well known manufacturers will give you similar performance.
Third party lenses are great values. The concern with Sigma and Canon is that sometimes when Canon comes out with a new body, the Sigma lenses sometimes need to be rechipped.