Okay, here's a list of Easter Eggs I found in Just Cause 2 (Just follow the coordinates to find them):
Shark: X= 12665 Y= 22595. You should see a fin, swim under and you'll see it's robotic.
Bubble Blaster: X= 4245 Y= 25978. Look for a tower, and go to the top of it.
Beached Whale: X= 29601 Y= 31301
Unknown Island: At the top left-hand side of the map, you'll see an island that looks like an S. If you fly a plane towards it, an Electromagnetic Wave will cause your vehicle to crash. I don't know if it's for some kind of mission or something, but I thought it was epic.