I'm just wondering, is there a mod out there that makes the entire area of the game available after completion similar to all other AC games? I've searched and can only find a few for skins... any one know?

Can't you just go back in the Animus and continue exploring? I don't recall the map being unlocked in any of the games, though the main quest is usually the last thing I do, so I usually have the map already unlocked.

No, in AC 1 after beating the game you can go back to the Animus but only into memories, there's no free mode, so in the memories you are limited to the weapons and skills you had at that time as well as the area you were allowed to explore...

You can load the last memory in Jerusalem where everything is unlocked (weapons, locations, etc...).

Hmmm... that must be different than the PS3 version because I remember trying that and there was still places in teh citities I couldn't go because of the dumb memory blocking thing

That's impossible, there are no more targets left. On Memory Block 6 you have everything unlocked, all three cities, Masyaf and the Kingdom to explore, best weapons and max throwing knives. Only once you attempt to kill the 'fake' Robert the map becomes limited to the road to Arsuf. To avoid it, just don't complete the mission and do whatever you want.