I don’t have an iPad but the brand new “Atari’s Greatest Hits” app looks like a blast. From touchArcade:
By way of in-app purchases, Atari’s Greatest Hits can deliver to your iOS device up to 99 more games from the historical studio’s back catalog, a mix of both arcade and (then) cartridge-based VCS / 2600 releases that you just might’ve grown up with. These games can be had in four-title game packs available at $0.99 each, as well as in a 68MB lump download of the entire library for $14.99.
100 classic Atari games for iPad