If you want to stick with Canon branding.. the EF-s 17-55 2.8 is really your only option. and actually a better option (optically) for your Rebel than the 24-70L
but will be a waste of money if you ever think you'll move to a FF sensor at anytime.
If you are willing to go with third party, the Sigma 24-70 is widely regarded as being a better lens, for roughly half the price.
There a some 28-70mm 2.8L's floating around on eBay that are EXCELLENT lenses (if you get a good one), but are designed purely for film..and not the best on the crop sensors...but stellar on FF cameras. They go for between $600 and $800 on eBay.