"Super Smash Bros. Brawl"
The Wii entry in the "Super Smash Bros." line of games is a button-mashing fighter that usually pits a room full of players against each other in an all-out free-for-all. However, the game also includes a team play mode that allows you to play with a friend to try to take down two computer opponents together. In this mode, you do not have to worry about hitting your teammate, as friendly fire is disabled, so you can concentrate on teaming up to take down the computer.
"Rock Band"/"Guitar Hero"
The "Rock Band" and "Guitar Hero" series of games both have several iterations on the Nintendo Wii, and all of them offer cooperative play. In each of them, players take on the role of singer, lead guitarist, rhythm guitarist, bass guitarist or drummer as your newly formed band hits the road and tours the country gaining fans and unlocking new songs. Players are also able to help out struggling bandmates with a burst of energy.
"New Super Mario Bros. Wii"
"New Super Mario Bros. Wii" plays much like the original 2-D side-scrolling "Super Mario Bros." for the original Nintendo Entertainment System with one big exception: cooperative play. Up to four players can take on each level at the same time, either helping or hindering each others' progress. Players can bounce off each others' heads to reach areas that are too high for a single player to get to or hop in a bubble to have other players help guide them through the level.
"Donkey Kong Country Returns"
Like "New Super Mario Brothers Wii," "Donkey Kong Country Returns" goes back to its side-scrolling roots but adds a cooperative play option. In this mode, one player takes control of the eponymous Donkey Kong, while the other controls his friend Diddy Kong. Each has their own abilities, and the Diddy Kong player even has the option to ride through the level on Donkey Kong's back, shooting peanuts out of a pop gun and giving the first player a hovering ability.