IMO-anything submersible. My favorite is a flounder gigging light. They put out a lot of light probably more than anything else you can buy. Also, I like the Starfire Q-beam at Wal-Mart. A friend of mine made his own set of lights that runs off AC with a generator. Those lights will light up just about the whole lake, but all of his stuff takes up a lot of room.
Good Luck!