Team Fortress' 15th Anniversary Gift Thing
Oh, I guess this is just about expired, but there's probably still time to get on Team Fortress 2 and receive your party bag for the 15 year birthday hurrah of Team Fortress. Yes, it is that long since the class-based mod originally appeared, spawning an entire sub-genre of FPS, and some of the most popular games of all time. If you log into TF2 before the 24 hours expires (I am not quite sure how long is left) you will get a party hat (obviously), a noise-maker, and a free cake (remodelled health pack). Mmm, virtual.