[Jonny]

I have the rebel xt, and I did a lot of research before finally getting the 70-200 f4/L. By far in terms of price to proformance. Then you can pick up the 1.4x teleconverter, and with the 1.6x crop factor coupled with that, the 70-200 becomes a 100-450 35mm equivalent.

Another plus is that the 70-200 f4 is way lighter and smaller than the 2.8 version (which costs about a grand).

So, the 70-200 f4/L is my choice.