[ChrisRabior]

No matter what anyone says, the 18-55mm kit is the cheapest 'wide angle' lens you can find. Yeah, it's not the best in terms of quality compared to an L series, but it's still a good lens if you use it in the conditions it was designed for.

In the grand scheme of things, you could probably get away with a number of lenses that fit your description..
canon's 17-85 IS, 28-105, 28-135 IS, 28-85
tamron and sigma also have a range of lenses that fit the bill.. 18-200, 28-300, 17-70, etc.

My advice to you is to buy your lenses to match what you're shooting. Take me for example. The sigma 28-70mm f/2.8-4.0 lens and the canon 75-300mm f/4-5.6 (nonIS) that I bought were literally a waste of money. The sigma doesn't hold a candle to the 28-75mm f/2.8 it was replaced by, and the canon isn't nearly as fast as the 70-200mm f/4 I'm planning on moving up to. If it was me, I would probably go for something like the 17-85mm canon lens.

What it all comes down to is that you're the only one who really knows what it is you want. 17 isn't wide enough for me, which is why I want a better wide angle. 28 may be fine for you. the 85 would work enough for me most of the time, but you may want to go up to 135. The best thing for you to do is to go to a local camera store and test out the lenses you think you may want to get with your XTi.

If you're not entirely sure on what you want, you can't go wrong with the plastic fantastic, aka nifty fifty, aka Canon 50mm f/1.8 prime lens.