If you're gonna get the 50D, don't get the 18-55. That lens is a piece of crap, it's pointless dropping money on an expensive DSLR if you just buy crappy lenses. The 28-135 (one of the kit options) is a really good option (if you want wider than that there's either the 17-85 or the 15-85), but if you want the absolute top quality you'd have to go for an L lens (24-105 and 24-70 are good walkaround lenses...they just make a huge impact on your wallet).
Hope this info helps!