My favorite iPhone apps are generally free. Not just because they're free, but somehow the free onces (Facebook, Mint, Amazon, etc.) are useful. Anyhow, the new Maktub iPhone app is free ... and it's fun. You can listen to all the tunes from FIVE, see pictures from the recording session and Twitter action from band and fans. You can even post comments to the app. But probably the coolest part are the slide puzzles made out of alternate album cover art -- these are comps that Charles Whiteside proposed before we settled on the final design.
Go get the app, write an review and pass it along to your friends.