I've got the chance to pick up a used 200 FD 2.8 lens for my digital rebel at a fairly inexpensive price.
I shoot mainly sports and portraits, so the 2.8 would be fast enough for me, but I'm concerned that being an "FD" and not an "L" lens it wouldn't be any good.
FD (old) lenses don't fit on EF (new) bodies. You need an adaptor to make it work and they are all very low quality. They require an optical element and will degrade the image quality. It will also be manual focus and manual aperture.