Freeverse, the people who brought you Marathon: Durandal XBLA, are currently offering one of their iOS games, Warpgate, for free on iTunes. Its available for both the iPhone and iPad. The iPad HD version normally retails at $7.99 which is at the high end for iOS app games so getting this for free is a bargain. It's free for a limited time only so be quick.
As you would expect it is littered with Marathon references. Landing on one planet which trades in wrecked space craft I am offered: "Colony Ship for Sale, Cheap! Contact R. Blake on Tau Ceti for more info." And if you are rich you can get your hands on a Mjolnir Battlecruiser.
I'm sure they'll be a Jjaro Dreadnought hidden somewhere. ;-)