Pirates of the Caribbean for x-box. Just pirates of the caribbean, released before the second movie. Got very poor reviews, but I loved it. It was only losely based on the PoC storyline (the black pearl turning up occasionally, and having a part in the storyline, none of the characters involved) but it is one the the best nautical games I've ever played, with all the various countries, combat FAR superior to Sid Miere's Pirates! (both on sea and sword fighting), RPG elements, allowing skill progression and ability unlocks, such as a 180 degree turn (a la movie), instant cannon reload, etc. Wide variety of ships, and more to the point realism within the ships, for example a spanish ship is tougher with more cargo space, whereas the english version of the same chasis is faster. Ability to choose cannon weight, affecting damage, range and reload times, different ammo types, realistic boarding (you don't just ram them, you have to get close and use grappling hooks), crew hiring and morale, the ability to hire officers to aid you on your ship, or assigned to their own ships, which will help you in combat, the ability to join in with large fights (picking a fight with two full squads of four ships, both from countries who don't like you, duking it out is fun.. just don't sail between them), attack ports by shooting out the cannon emplacements then attacking on foot, pistols that pack a real punch but slowly reload, different sword types, and the ability to explore islands for treasure. (And undead monkeys. Which drive you nuts.)
Bloody marvellous, pick it up if you see it, can't be expensive now.
Might be on the computer as well. Box looks like this:
http://ecx.images-amazon.com/images/I/51PNHSKEM5L._AA280_.jpg
And it's Bethesda. That gets it brownie points for any free-roaming game.