I'm perplexed and fascinated with GBA4iOS - a Gameboy emulator for iOS that exists outside the App store and doesn't require any jailbreaking. Somehow changing the date on your device allows these custom plist files to be installed. I'm not sure how that works (hence being perplexed) but I love that someone found a way to open up the full world of emulators and ROM's to iOS devices (hence the fascination).

So, just pair this up with sndtst and you're fully covered in the nostalgia department.