bigfrog23:but there are 2 main draw back to the sigma 50mm Macro lens and that is that the lens changes in length as it focuses which can make it a pain to work with. Also the other disadvantage to this lens is that if you have auto focus turned on you can not focus the lens manually it must be set to manual focus to focus manually.
Vs. the 60mm macro lens which does not change its length even when you focus to 1:1. and you can manually focus the lens even when auto focus is activated. i think that these to thing are worth the extra 50-100 hundred dollars for the canon lens and that is the one that i went with got mine on ebay for around 32o bucks new.
These are excellent points

I know I wouldn't give my 60mm up while using my 20D!