I have used these guys before, the Assassin's Creed III I gave away last year I bought from there.
Their prices aren't always amazing, but now and again some gems appear, and they have for Batman:AO which has now had most of its bugs fixed.
Looking through my other lists to see who else to recommend.
Global Games are doing it for just over £10 with the Deathstroke DLC Not used them up so far they have 181 positive feedbacks on a site I use.
* Updated game trainers and cheats daily
* Get notified when new cheats are added
* Request which games get new trainers
* Priority support with any problem