You did not mention if you were thinking of trading up to a FF body or not, cos' if you are then you should seriously consider the trade off between the EF-S 17-55 2.8 and the EF 24-70 2.8L.
Now I've seen some great pics and amazing HD video taken with the EF-S 17-55mm lens and I struggled with the choice between this lens and the 24-70 L, especially as I do a lot of video stuff on the streets, but 2 months ago, just a couple of days before Christmas I succumbed to the 24-70 f/2.8L which incidentally was only 100 euros more than the EF-S 17-55 (1000 vs 900 euros)... and I have to say that I'm glad that I did because the colour it takes requires almost zero correction in post & speed of AF is stunning.
Okay I get around the non-IS issue by using a monopod for video, but for handheld photos I always shoot in manual and set my aperture first if daylight/bright or shutter-speed first if ambient light is an issue and you can easily get away with 1/25th of a second on the L lens if you lean up against a lamppost or wall etc.
Neuro is dead right that on paper (at least) the EF-S 17-55mm 2.8 on a crop is technically a better lens not just IS but possibly sharper too, but for me the 24-70 is a keeper lens and should outlast several bodies and I love the colour it produces.
I also have the canon 50 1.4 and the IS version of the 70-200 f4L, and even though the latter is way sharper than the 24-70mm it seems cold (blue sometimes - have to adjust RGB curves in PS) when compared to the 24-70 2.8L. My 50 1.4 seems neutral color-wise, but the 24-70mm feels 'warm', dunno' does that make sense