This is Canon's most expensive midrange zoom designed exclusively for the 1.6x sensor cameras. It only works on the 30D, 20D and the Digital Rebels (Rebel (EOS 300), Rebel XT (EOS 350) and Rebel XTi (EOS 400). Forget it for film cameras, full-frame and 1.3x digital cameras.
It will cost you about a grand. I'll cover if it's worth it at my recommendations at the end. Read the full review here