I just got the Rebel XTi and have been hankering to take long-range photos. I'm not quite sure what I'll use it for exactly since I'm still playing around w/ the camera. Probably some wildlife/nature ...
As people have said its a tough choice. I have access to the f4L and its a stunning piece of kit, its pretty sharp at f4 which the 70-300 prolly wont be, you NEED IS at 300mm especialy at f5.6, and ...