mario kart ds
A kick ass game for the Nintendo DS, released on November 14, 2005 for the US and December 8 in Japan, it was also the first game (along with Tony Hawk's American Sk8land) to make use of the DS's wifi capabilities. You could race online with up to four players in 16 of the 32 tracks.
Because this was Nintendo's first foray into online gaming, the online part of the game had a couple minor issues. For one thing, there was no way to communicate. Also, you could not trade friend codes in game, which meant if you found someone on Worldwide mode with whom you had a really fun time, there is no way you will know if you will play them again. Despite these and other small problems the game still kicked ass.
Mario Kart DS might be described as the best WiFi game released to-date.