Battleships Extreme.
Classic battleships game gets a 2006 makeover as part of a Navy recruitment drive in Australia. Comes with cool extras like mines, torpedos, etc.
 

Bejeweled Valentine
Bejeweled for lovers! Temporary Valentine edition.
 

Big Monster Battle
Pick a monster, pick a place, pick a fight! The first fighting game hits Messenger. Select a sequence of moves and try to beat your opponent in this monstruous variation to the classic rock, paper, scissors game.
 

4Across Birds
4 Across... with birds ! Available via the Danish Sporkle portal, free trial for 5 days.
 

Checkers Classic
Challenge your buddy to a game of Checkers.
 

Dead Man's Tale
An interactive online adventure, based on Walt Disney Pictures' Pirates of the Caribbean: Dead Man's Chest, that allows users to earn a berth aboard Jack Sparrow's ship, the Black Pearl. (Requires Windows Live Messenger 8.0.0787)
 

Gwaam
Gwaam is a guessing game in which you have to pick a blue or yellow "Gwaamian" within 20 seconds and then hope it'll be the least featured color in the area.
 

Minesweeper Flags
Play a head-to-head version of classic Minesweeper.
 

MSN Soccer Challenge
 Take or avert free kicks near the goal. This game is entirely in German but you should be able to work out the gameplay nonetheless.
 

Pegball
Play a board-game-soccer match with your buddy. Available via the Danish Sporkle portal, free trial for 5 days.
 

Cobauw Penalty Game
Penalty shootout game with terrible graphics. It's Dutch, but you'll get it.