While the future of emulators on iOS is looking peachy-keen if you’ve got a Mac and aren’t afraid to compile some source code, if you’re still not willing to jailbreak your device or go to Android for some sweet emulators, Nintendo DS emulator nds4ios is available right now without any relative tomfoolery. iEmulators has an enterprise-signed version of nds4ios that you can install right now without jailbreaking. You just need to go to their site, tap on “Apps," scroll down to nds4ios, and install it. Apple hasn’t revoked the certificate yet, so have at it!
Do note that if you’re going to use ROMs on this – preferably ones that you’ve backed up yourself, like I have (and I’m not kidding, I’ve backed up my entire GBA and DS collection) – you’ll need to zip them up and add them from Dropbox or GoodReader or something similar using the iOS “Open in…" dialog. Also, you’re trusting your device to install an app from a Chinese developer’s enterprise certificate. So if your desire for security is trumped only by your desire for emulators, then bombs away.