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.
The 17-55 f/2.8 IS is the best general purpose zoom for an APS-C sensor. Very sharp, image quality is just as good as an L lens, and the IS works very well. They can be had for $800-$900 used. Only thing I don't like about it is the focus ring location and the size of the focus ring, but other than that it's an excellent lens.
its an older lens, but still one of my favorites. Tamrons 28-75mm f2.8
amazing lens, about 1/2 the size and 1/2 the weight of the canon 24-70mm. doesnt have the build quality and weather sealing, but for every day photography.. for the money its an amazing lens.
If you want full frame compatibility and don't need the wide end that desperately, you can wait some and then get the new Tamron 24-70/2.8 - it's just dropping in price, in contrast to 17-55/2.8 it has weather sealing and good build quality and esp. on crop its center sharpness is good. See this thread, too (nicer forum around here, but anyway): http://photography-on-the.net/forum/showthread.php?t=1145772&page=32