Defender Chronicles - a tower defense game that's different than most. Looks better, feels different, and has "heroes" with levels that you can build up and get better gear for. A cross between tower defense and RPG I suppose? I played this game for much much much longer than any other.
Words with Friends - fake Scrabble that's free. Awesome.
Scrabble - real Scrabble. Awesome.
Word Warp - good for training your brain for Scrabble.
Plants vs Zombies - second best tower defense game I've ever played. Probably because it didn't feel like a tower defense game.
Final Fantasy - yes, it cost $8.99 so it's pricey for the iphone, but I loved playing it again 20+ years later. And it's improved from the original NES version ... I think it's the same as the GBA version called Dawn of Souls, but I'm not sure.
Honorable Mention: Tetris, Bubbles Lab, Street Fighter 4. There's a bunch of others that I played until I "finished" them and then moved on. Geodefense Swarm was one, 7 Cities TD was another, and I forget the rest.
ESPN Scorecenter or Sportacular
Wikipedia (love love love this)
Top Shelf (best bartender app out there, imo)