Well, you can get a good starter lens for ~$300-$400 like Tamrons 17-50 f/2.8, . The kit lens takes up $100 in a budget anyway. I'd suggest just to get a better lens and a lesser camera, than the other way around. If a better lens isn't in the budget, chop the budget allotted to the camera to make up the difference. What budget are you set with?

Getting used gear is often a way to get great performance on a budget. KEH.com sells used gear and is very clear and thorough in their condition descriptions, you could reasonably get a solid performing, fast aperture starter lens on there for less money. I use them and they are a commonly used retail for many pro's, almost as synonymous with online photo gear as B&H Photo.

I would way rather have a Rebel XT and an 17-50 f/2.8, then a Rebel XSi and the kit 18-55, and the XT could save you $2-300 on camera body over XSi.

The Tamron 70-200 f/2.8 is ~$750. You don't have to spend that much to get a similar lens. I own the 70-200 f/4 minolta for that purpose (what shot the dragonfly), and you can find those for only ~ $250 (really its a steal at that price too).

The best cost to optical quality you can get out there is the nifty fifty, Canons is the 50mm f/1.8, its ~$100, and will optically match most lens under $1k, and do many things most other lens cant. Its an excellent portrait lens. If the budget is super tight, I would at least get the kit with that. The 50 is what I started on, and to this day is one of my favorite most useful lens'. (its also very small, which is nice, as big lens get obnoxious to lug around). The 50's also have super zippy fast AF.