Actually, what I think you've got there is a bullfrog.
I probably don't sound like I know anything (and those who know me will probably be surprised) but I actually do know a little about bullfrogs, as I raised two from tadepole-hood.
I lived in Philadelphia at the time and I actually got it confirmed that mine was a bullfrog by one of the managers at the amphibian exhibit at the Academy of Natural Sciences. Yours looks nearly identical to mine when (s)he was a tadpole and it looks the same as mine in adulthood.
If you want to know more about bullfrogs (and LauraFrog was right-- it is a Rana species, Rana catesbeiana ), these are two excellent sites:
http://www.fs.fed.us/r4/amphibians/bullfrog.htm and
http://www.critterzone.com/magaziner...atesbeiana.htm
(Edit: Sorry for the awkward wording, I'm feeling kinda brain-dead today ._.)