A few months ago SN Brussels Airline launched a nice and engaging viral (it's still on) which allowed users to personalize their ads. Now they are again online with a smart online competition focused on word of mouth.
Take a break now (in French) allows people to win a week-end in one of the cities served by SN Brussels Airlines. The game mechanism is really cool: entrants submit their profiles and an appealing presentation explaining why they would like to win. The airline then selects every week 20 entries and publishes the profiles on the site on Wednesday afternoon. And here comes the viral idea: site visitors are asked to vote their favorite profile, therefore deciding who's going to be the winner. In this way the selected people will spread the word about the competition inviting friends, relatives and colleagues to vote for them.

The cool thing about this initiative is that the winner will receive a phone call on Friday and he will have just a few hours to get to the airport and leave for his free week-end. An excellent example of viral marketing.