I agree with everyone who recommends good glass first. That's exactly what I'm doing. When it comes to upgrading the body, I think by the time I get the lenses I want my skills will hopefully justify buying a much higher level body. I'd still keep my XT as a 2nd body of course. Cameras are like bikes, you can never have too many. 
If the OP really wants to upgrade - 20D/30D would be the upgrade in this example.
