just bought a rebel xt

[Tiberius47]

What kind of flash would you recommend as a general step up from the built in flash on the XT?

The 430EX is a very popular flash for Canon users. Just make sure that you get a flash that has a tilt and swivel head, makes it much better for bounce flash. Don't get a flash that you can't tilt and/or swivel, because that will limit you to direct on-camera flash only.

Polock, the Tamron 17-50mm f2.8 zoom is a nice lens, I have one and it's nearly always on my camera.