The Super Bowl packs the stadium, sees the most HDTV sales of the year, and has advertisers drooling over the $3 million 30-second TV ads that run during the commercial break – and now it’s a social media phenomenon, too. Advertisers are flocking to Twitter to run innovative campaigns during the weeks and months leading up to the Super Bowl, offering hefty prizes in an effort to augment their TV presence.

USA Today reportsthat all of the 68 30-second advertising slots for the big event itself have sold out on Fox, but that isn’t stopping advertisers from attracting viewers through social media.

Two Twitter-based Super Bowl campaigns stand out as being extremely high-stakes, but (as with any bets placed on the underdogs) offering a potentially high reward in return.

Mercedes-Benz and Audi, two premium European car manufacturers, are both putting their faith in Twitter as an effective marketing tool alongside their coveted Super Bowl TV ads.

Mercedes-Benz is unveiling “The World’s First Twitter-Fueled Race,” a contest that will award two new cars to the two-person social media team that can rake in the most tweets, follows and overall attention for the brand up until game day.

Stephen Cannon, marketing vice president at Mercedes-Benz, talks about placing his trust in Twitter:

“We’re using the 2011 Super Bowl as our head-long plunge into committing to social media. It’s our strategic leap of faith.”

Audi is running its “Audi Inner Circle” social media campaign, rewarding its ten most active social media participants on Twitter, Facebook and elsewhere with big prizes, like all-inclusive trips and other similar prizes.

We’ll see how these campaigns, with their ultra-luxurious rewards for power-social media users, pan out on Feb. 6th.