Head on over to the Retro and Contemporary Game Archives–a blog run by the equally wordily-named ‘Satoshi Matrix’–for a quick run-down of some of the more worthwhile hacks, mods, translations and homebrew titles for the NES. Most will have to make do with an emulator in order to boot up these ROMs, but this shouldn’t be too much of an obstacle; with a good USB controller you’re probably better off!
Two of the most eye-catching games on the list are two fan translations of Japanese Famicom exclusives: the ‘original’ Final Fantasy III Hudson’s Adventure Island 4.
You might’ve seen Rockman no Constancy before, but it’s probably a safe bet that you haven’t seen all of the Rockman Endless hacks (2, 3, 4, 5)! These titles turn each of the respective (Japanese) Mega Man titles into an endurance game like the mode featured in Mega Man 9 and 10. Remember that each of the zip files linked are patches that need to be applied to Rockman , and not Mega Man.