Stop whatever you're doing right now and go download You Don't Know Jack for iPhone or iPad, or in the free lite version if you want. I don't know of any game that, throughout the years that it's been available on various platforms, is more consistently enjoyable by anyone, from the most hardcore of gamers to non-techie trivia buffs.
You Don't Know Jack is one of the most solid gaming experiences around, and the brand new iOS version doesn't skimp at all. It's got hilarious iOS-specific audio (Host Cookie jokes early on that he's "glad to be hosting an app that's not a ripoff of Scrabble") and questions, all of the old mini-games (like Dis or Dat and the Jack Attack), and it even has the backstage talk and fake commercials that the main console versions have. Great game -- I can't recommend this one more.
OK, if I'm going to nitpick, I'll say that the graphics are just slightly pixelated on the SD version. And even the iPad version is one-player only -- the game recommends if you want to play with more people, you should buy one of the other versions. But there is Game Center integration, and with 20 full episodes available in the app (and even more promised to be coming soon), this is a terrific experience that won't disappoint anyone with a taste for trivia and/or a sense of humor. Great game, and well worth the US$2.99 on the iPhone or $4.99 on the iPad.