Phil,
I've heard the 17-55 IS is a beauty, but the dilemna is that it costs a heap of money for something that wont be useable with a full frame camera down the track.
The other consideration is the 24-105 is being offered as a 'kit lens' with the 5D so you can buy both together and perhaps save some money.
Personally, I'd wait and start saving those dollars
Terry