Have you considered the EF-S 17-55 f/2.8? It's a fantastic lens, I was looking into nabbing one of them down the road for my 60D. You'll lose 56-69mm with your current setup, but I would think that it wouldn't be too big of an issue.
Don't forget the Tammy 17-50 f/2.8 too. It costs significantly less than the 17-55 and also produces some great pictures.







that last one is outstanding 

