In the UK insurance company Norwich Union has just launched Memory Meltdown, a nicely cheesy advergame to engage users and drive policies' sales online. The game is promoted through email marketing and tries to take advantage of the viral effect also. The final prize is an holiday worth 3000 pounds plus a bonus of money to be spent during the vacation. The more friends you invite to Memory Meltdown the more money you can get for your vacation.
Memory Meltdown it's a funny experience, and it's really well done (by Soup) with great attention to the details (See for example the possibility to activate subtitles if you cannot listen to the audio).
The other thing I found brilliant are the Tv-like commercial breaks during the game.