The latest one is on an even bigger scale, and Massively has joined forces with Raptr and the Bounty Hounds Online team to give players the chance to win NOX headsets, a Razer mouse and keyboard, and piles of in-game currency for BHO. The event is divided into three contests, so you've got several different ways to win. There's a contest for captioning a screenshot, one for hours logged via Raptr, and one for pure random luck.
You can get all the details on the Bounty Hounds Online forums. The contest lasts until September 5th, so get your entries in and good luck!