If you are shooting a lot indoors, then the 17-55 f/2.8 can't be beat. The fast aperture combined with IS gives you the ability to shoot without a flash for most things. In my opinion it is the best general purpose lens for a crop camera. If you are just getting one lens, this is the one to get. I have several L lenses, and this is as good a lens as any of them.
I would recommend it over the 15-85 because I think you will find the 5.6 f-stop on the long end of the 15-85 a little restricting indoors (I don't like to use flash much). The difference in focal range isn't as big as it looks, and the constant f/2.8 makes a huge difference.
If you shoot more outside or really want a longer focal range, then I suggest the 24-105 f/4L. Indoors, it is just one stop slower than the 17-55 f/2.8, and you can usually get buy with bumping up the ISO one stop.
For the long end, I would get either the 70-300 L, or the 70-200 L (several flavors to choose from here based upon price and need). If budget is an issue, the non-L 70-300 is a good lens.