17-55/2.8 IS gets my vote as well. Excellent IQ and helpful IS as said before, but just as import.. 17mm at f/2.8 is just so nice indoors where you often just can't step back to get everything in the frame with a 24mm (my house has interior walls - a design flaw clearly). For the f/4 with IS argument.. IS doesn't stop people from moving so it's only half the solution compared to f/2.8 - and with the 17-55 you get BOTH 
