Bomberman GB 2
You don't need me to write about this do you? If you've never played B-man, well here's an excellent, inexpensive way to get acquainted with one of the most exciting and hilarious multiplayer games available.
Using a tap, up to four players can join in a massive blastathon pretty much anywhere. Or play at home on a Super Game Boy adapter for partial color. New traps should keep fans happy.