You can't go wrong with Canon Rebel XT, Nikon D-50, or Pentax K100d or K110D (cheapest of them all). These are the lowest priced models for each major brand. They all have similar features. The Nikon and Pentax allows you to buy used lenses even manual focus and use them (of course in manual). So they give you little more options than the Canon. But they are all so close in performance its really a toss up. Basically go to a camera store and pick them up. Check out the controls and how your hands fit them.
I say Nikon is the lens quality front runner. But since your on a budget you will not be buying the best lenses anyway. Canon has the advantage with new technology. But again since you are on a budget you will not be buying a new one every year. Pentax has the advantage on price. You get a good quality camera for a good price. The Pentax K110D is the lowest priced DSLR on the market right now from a major company. The K100D adds immage stabilization for about $100 more and may just be worth it.
For budget minded people who want to buy into a good "system" I think Pentax is the front runner.
And before you buy. Make sure you get one from a reputable company. Don't automatically go for the cheapest price. There are many stores that advertise a low price but then get it back with bait and switch tactics. Or if you refuse to buy any other over priced accessories or warranties (sometimes charge you for items that are supposed to come with a camera). An instock item all of a sudden is back ordered!
I say for a beginner the choices are in this order. For a person who wants to be a good photographer but not necessairly turn to a pro for 100% of income.
1 Pentax K100d.
2 Pentax K110d.
3 Nikon D50 (have one and works just fine)
4 Canon Rebel XT (have the next model up and also works just fine)
Choices for a beginner that will work hard to turn pro in the near future!
1 Canon Rebel XT
2 Nikon D-50 (very close even tie with Canon, reason Canon is first is I think they have better research / spend more on new technology)
3 Pentax K100d (very good camera brand but just short of full pro caliber right now).