Canon. Better lenses for sports. The rest of it depends on your budget.
The digital rebel is decent if you're on a budget, but for a few dollars more you can get the EOS 20D which is dope.
For a whole lotta dollars more you can get a $7500 (body only) EOS 1DS mark II which will shoot sequences and everything.
Lenses are key. The standard among all the photogs is the 70-200 f2.8 which is one of the most versatile lenses for shooting sports. You'll also need a wide angle lens to make people look like they're going bigger than they really are, and a lens in between for portraits.
Then you'll need a flash, another flash, a wireless flash triggering system, a tripod, more batteries, more memory cards, more.... you get the picture.
http://www.bhphotovideo.com/bnh/controller/home?A=search&Q=&b=8&Submit.x=13&Submit.y=10&Submit=Go&shs=&ci=6222&ac=