Been think about filling this gap since I got my 5D2. I have a Sigma 10-20 that I can still use with my 50D. And I have a Canon 24-70 2.8L; 70-200 2.8L; 300 2.8L and some other glass. Truth be told, I can't tell you the last time I have shot wide open with anything other than the 300 2.8 w/ a 2x (600 5.6) for birds.
That said, I keep thinking the 17-40 may be enough lens. Thoughts?
I should add that price is not an issue since I can't really afford either. But I will get one somehow. My wife says I always do!