I have the Canon, but for me it came down to cost between it and the Nikon. I did not look at the Sony, although I have heard good things about it. I don't know if the Xti is a huge upgrade over the Xt though. Yeah, you get more MP, but the sensor is the same size.
Btw, I got the camera w/ lens kit for less than the body itself retails for, so it was a pretty easy decision to go that way for me. Otherwise, I would have given more consideration to the highly rated Nikon.
The lens is ok. I will definately upgrade it at some point. First thing I bought was a 50mm 1.8 though, because at $80, it is a great deal. I use it all the time when doing shots of my 3 month old son. If you were to ask me, that should have been the kit lens.