My QB rankings put him at the top, followed by Rodgers (because there is NO other QB that could do what he did, while being smashed into the ground every other play), Brees, Favre, and Warner. After that, it gets murky. I've always felt Brady is overrated (with his supporting cast - and especially his O line - any halfway decent QB could become awesome), Rivers hasn't quite hit his stride yet, neither has Flacco, and I dare anyone to suggest Romo with a straight face. Or, even worse, Cutler - he's the twisted love child of McNabb and Favre, with all of their bad points, and under Lovie effing Smith. Ugh.
However, as good as Manning is, I think that Rodgers, Rivers, Flacco (and, I know this is heresy, maybe Sanchez) could eventually catch up to him in quality. Rodgers might do so as early as next year (although three is more likely).