It's a classic question....
I am a brand new 5D2 owner (thanks to Randy98mtu!) and I need a lens for it.... It seems like the two above lenses are the classic general purpose zooms to pair with a 5D2. I know the technical specs of each, and I can relate the field of view of each to my experiences with my Rebel and kit lens. The shallow DOF available with each is a little more difficult to wrap my head around, as the 18-55mm doesn't have much going for it in the "shallow DOF" department, although I do have the 50mm f/1.8 and 85mm f/1.8 to get a little perspective. However, I'm having trouble weighing the 105mm range and IS against the f/2.8.
Basically, what made you choose one over the other for your full frame DSLR?
I've never used a full frame standard zoom lens, and after getting my 50L, I have no desire to.
All 50mm lenses sing on 35mm format!