Yea, that would be a fun one. I'm going to pick up the 18-55 by the end of the year also, but that will be it until I get a new camera (I have Nikon now, but will be getting the Canon 40d, so I'll need all new lenses). When I get a new camera I'll be getting the 24-70 2.8 immediately to go with it. Then of course I'll eventually need a 70-200 and would love a 12-24 for the opposite end.
Curious: Why are you making the switch to Canon?
I have the 18-55 VR and 18-200 VR, but a wide angle would be heaven to me.
I've heard awesome things about the 70-200 or was it the 300? I can't remember between brands. lol