Spellitaire arrived on the App Store last month as the first offering from Knucklehead Software, a studio consisting of two developers who've formerly worked for places like Valve and Blizzard. It's a simple game, which basically replaces the cards in solitaire for letters, which you then use to try to spell words and score as many points as possible within a five-minute time limit.
I like it for its simplicity, though -- some word games can get frantic or complicated, and this one basically sits back and lets you spell whatever you can think of within a very generous limit.