This little app combines pretty much my two favorite things right now: my copy of Halo 3 and my iPhone. iHaloStats pulls all of the information from your Halo 3 matches available on Bungie's site (and if you haven't played the game, yes there is a ton of it -- every shot, grenade throw, and double kill is tracked for you), and puts it all in a convenient, if a little complicated, format on your iPhone. All of your ranks, kills, skills, medals, and promotions are all there.
And in fact, it's not just your info -- you can punch anyone's gamertag in and instantly see how far they've gotten in game. Is your friend bragging that he finally beat it on Legendary? Dial him up and check out that claim with ease.
Very impressive, and to tell the truth, I'd like to see more tools like this (maybe even some official ones?) to extend the various games we play. Considering how tracked and connected videogames can be nowadays, it's exciting to see possibilities like this arising.