Letterpress is the latest app from developer Loren Brichter, creator of Tweetie and inventor of pull to refresh.
It's a mix of Scrabble and Go, and is a lot of fun. Plus, it's a well-designed app that takes advantage of iOS.
It's free in the App Store, with a 99 cent upgrade to the full version. Give it a shot. The wife and I have been playing it all day.