Canon EF-S 17-55 F/2.8 IS USM hands down.
+1. It's a direct replacement - basically the same focal range, but faster, constant zoom, better bokeh, faster and more positive focusing, full time manual focus. It's a whole different league (as I found out today - I just got mine. It makes me feel more like a "real" photographer too
).
But I agree with what's already been said - the 188-55IS for the money is quite decent, and it's perfectly possible to get great shots with it. If you are finding your shots lacking, my gut feeling says that a new lens isn't necessary going to be a magic fix (though of course it's difficult to say without knowing your level and seing some example shots.)
To be honest, unless you've got plenty of money to throw around, I wouldn't even recommend investing in good glass until you've used your gear to death, got the most from it and now *know* exactly why you need better glass.


