What Canon EF L series lens should I get for my Digital Rebel?

Hi.
I dont knowe wat lenses canon hawe I hawe Nikon myself but i think they hawe something around 55- 200 that is a wery good lens I use it my self and one 18-50 and i am very satisfied with them.

It depends on what you shoot. For wild life a long telephoto zoom like the 100-400L IS is very convenient. Note that this is a f/5.6 lens (at 400) so is not particularly fast but it is very sharp and the range is very convenient. I've rented this lens a few times and I've always been happy with the results.

If you prefer a fast lens the 70-200/2.8 IS is probably the best zoom made by Canon. Very sharp, fast, well made and favored by professionals.

Those two lenses are expensive and heavy. If you prefer something lighter:

The 70-300 DO IS (strictly speaking not an L lens but close enough) is very light and convenient, especially for travel.
Not cheap though.

And finally the 70-200/4L is cheap, is not nearly as heavy as the 2.8 lenses, and takes great photos. It doesn't have image stabilization so you'll need to use faster shutter speeds than with the previous lenses, or use a tripod.

I personally own the 70-200/2.8L IS and a 75-300/4.0-5.6 III lens. The 75-300 is nowhere near the quality of any of the previous lenses, but it is very light and easy to carry.