Well for me, I started off with Nikon, used the D90, then switched to Pentax, used the K-x and K-7, and finally went to Canon and used the T2i, 7D then 5D Mark II.
Out of all the cameras, I would say that the 5D Mark II cured my gear lust. It actually made me feel content with the type of lenses that I had. It was THAT good. All the other camera bodies just made me want more and more. And I think that's the problem with the Rebel Series. It gives you a taste of what's better out there. I really think if you have the budget, go for the best body you can buy. That way, you won't have to waste money upgrading it when you finally reach your full potential.