As far as relatively inexpensive, but still pretty good, lenses go, the 55-250 IS zoom is a good lens for the price (I shoot almost exclusively with this lens on my XSi right now), and the 50mm f1.8, at under $100, is also often recommended as having good IQ (image quality) for the price. Beyond that, you'll find that pretty much all of the other lenses that are out there are very pricey, in many cases more expensive than the camera itself.
If you're doing a lot of indoor shooting, you'll probably also want to invest in a good flash, since the on-camera flash can be very harsh. Canon makes several, and I believe the speedlite 480EX can be found for under $250. You might also want to invest in a decent tripod (no recommendations from me on that front, I'm using an incredibly cheap and insufficient tripod at the moment) if you plan on doing landscape photography or nighttime/lowlight stuff like fireworks.
In order to get a wider angle, you'll have to spend a pretty decent amount of money - I don't believe Canon (or the 3rd party lens manufacturers) has an inexpensive wide-angle option out there that has good IQ, but if I'm wrong someone here will correct me. 