Aji's iPhone word game Lexel [App Store] offers a nice and free (for now) variation of your standard word game.
Like all word games, the goal is to simply create words of 3 or more letters. Lexel, however, adds a twist by requiring you to move the letters around on a limited grid in order to form words.
Letters continue to appear randomly on the screen so you need to be quick to form words before the screen fills up. Tiles also can only "slide" around on a grid and must be moved around other pieces. This adds a spacial component to the game that actually works quite well.