wow, i am quite overwhelmed by the responce to this question, however, i am not sure what i want to do, this is my big dilema, but i would have thought that i will be covered from 17mm right through to 400mm with 2 excellent lenses, then all i would need will be a macro lens later.
@diego thank you for an excellent insight into these lenses..
@tim thanks for the link, learned you need to turn off IS when tripod mounted, good tip..
@RTS lens looks great on your 20D, but at £1600, its too expensive..
but as i have said before, there is no rush for me, it will be a xmas pressie, so i will continue to watch with baited breath as sigma and canon roll out new stuff ..