Epoch.2 is a well rated iPhone, iPod and iPad game that costs anywhere from $2-$6 normally on the store (currently it's priced at $4.99).
“EPOCH has trekked across a war-ravaged country to find the one person he was programmed to protect: the Princess, Amelia. Now he must follow a final, desperate lead to reach her, with the two warring robot armies of Omegatroniks and Alphetekk standing in his way. But what surprises await EPOCH when the Princess is finally located? And what will she make of the world she wakes up to?”
You cannot get it for free as the IGN free game of the month (link). But you have to go through this link to claim your redemption code.