Bob mentioned to me that Sigma has some good alternative lenses to Canon, the folks at "Lightrules":http://www.pbase.com/lightrules/lenstests have some reviews of these lenses comparing them with Canon. Interesting results , but as Bob also mentioned, quality control is much nore of a factor with these lenses, so caveat emptor

* "Sigma 24-70 F2.8 EX DG":http://www.pbase.com/lightrules/2470. This is comparable to the very good Canon 24-70 L, but it costs $365 vs.$600 for the 24-70.