The latest and greatest from Canon is probably the 5D - 12.1 MP and full-frame. You can get a bundle of this camera body and the excellent 24-105 F4L lens for the bargain price of $3800.
Ok, back to reality, the 30D is currently the top of heap for Canon's non-professional line. The 30D is more semi-pro, while the XTI is more for the general consumer market.
There are SO many decisions to be made with respect to lenses, and most serious photographers have a bag full of them for various types of shooting. If you're serious about photography (for this post, I'll assume you are), think about what types of subjects you'll be photographing, at what distances, and what level of quality to you require. With lenses, you largely get what you pay for. Some are better values than others, but for the most part, quality glass costs more $$$.
A complete lens bag has zoom lenses covering a broad range of focal lengths, maybe with a little overlap, plus a couple of primes (non-zooms) for specific purposes. Generally, most people would start with a standard zoom as a walkaround, then a longer telephoto zoom for extra reach in other situations. Reefkeepers like us tend to add a Macro lens for tank photography. Next you might want a fast prime for shooting indoors without a flash. How about an ultra-wide angle for architecture or landscape? Then maybe a super telephoto. See where this is going? Lots of choices and decisions to be made.
As someone starting out, you don't have to make all of these choices today. The kit lens may be perfectly adequate for you initially. I could hand you a $1200 L lens tomorrow and you won't necessarily take better pictures with it. The lens certainly has the
potential to take better pictures, but the person standing behind the camera is often times the limiting factor.
FWIW, I've been into photography for a while now, and the 18-55 is still my only lens in that range other than a 50mm prime. I find that I just don't use it very much, since most of my shooting is either wildlife with a 70-200 F/4L, or tank shots with the 100mm F/2.8 macro (both great lenses, btw). I am at a point where I am ready to replace the 18-55, because I can see its shortcoming in the pictures I do take with it.
My best advice is to think about what types of lenses you're intersted in (standard, tele, macro, etc.), what your budget is, and then ask for specific recommendations. It's also worth noting that a cheaper camera with quality glass will generally outperform the most expensive camera body with a cheap lens.