iPhoneNES is a NES emulator for iPhones. NESApp seems to be iPhoneNES but updated more regularly on its primary homepage with the same authors.

Changes since v0.37:

[nervegas] Fixed default sound preference issues
[nervegas] Save game state and preferences on “home” button press
[nervegas] Fixed rom deletion (would delete from list, but not file)

http://iphone.natetrue.com/nesapp/