If you can afford f2.8 then go for it, significantly faster than f3.5 and upwards. At the end of the day it comes down to what you want to get from the lens, and more importantly budget. I use the Canon 24-70mm f2.8L lens which is fantastic, but comes with a high price tag. It also has limitations at the wide end on a crop sensor - it is not nearly wide enough. When I need wide, I use a Canon 10-22mm f3.5-4.5, again a fantastic lens.
As suggested, I think the Canon 15-85mm f3.5-5.6 IS may be a good option, but I think this has a rotating ring during focus, if it does, then this is a negative.
My recommendations would be:
Canon 17-55mm f2.8 IS USM, or (and I'll probably get slated for this) at slightly less of an angle, but makes up for it with zoom and should be a half decent 'walkabout' lens until you out-grow it, would be the Sigma 18-250mm f3.5-6.3 DC Macro OS HSM.