The 17-55 IS is the best normal zoom you can buy for an APS-C sensor camera. f/2.8 and IS make it unbeatable in low light if you have to have a zoom.
That said, it's up to you whether the price tag of $800+ used or $1000+ new is worth it. Image quality wise, it will be sharper than the 18-55 IS, but you may not notice a whole lot of difference unless you're viewing 100% on your monitor or printing very large.
The caveats with the 17-55 are the rather mediocre build quality (considering the price), incompatibility with full frame should you ever upgrade your body, and a widely identified dust problem. Many people on POTN refer to this as the "dust pump" since dust easily gets inside the lens.
If you need the f/2.8 on a tighter budget, the Sigma 18-50 f/2.8 EX Macro and Tamron 17-50 f/2.8 XR Di II are both good alternatives. Neither are as sharp as the 17-55 (naturally, given the price gap), but unless you really need supreme sharpness throughout the image at f/2.8 then you probably won't find this a big issue.