For those of you with iDevices, I recently discovered this chiptune player on the App Store. It supports NES (NSF), SNES (SPC), Genesis (VGM), Gameboy (GBS) and zipped files of the above.
You load files on to it via the interface in iTunes. In my experiences a bad file may force the app to crash on startup, but the sound output seems accurate.
Edit: It's $2, but well worth it IMO!