Twitter and Facebook. If it gets viral there, it will go wild. Just need to maintain 5-10 accounts to give it initial push by retweeting. Rest depends on your quality of contest to create buzz.
That's the kind of contest might appeal to users of this forum, you should do an ad buy with DigitalPoint to promote it.
advertise in college newpapers. It is very inexpensive. And college kids need money. That just triggers some new ideas.
Press releases, social networks (Facebook, Twitter), social bookmarking sites, forum signatures, blog posts...
Word of mouth is always a great way, a viral you tube would push it to great heights. What is the ranking and how much competition do ya have?
As suggested go whit social media and hope it goes viral . A well executed YouTube video will also help a lot .
You know, people underestimate the power of online classified ads - you should try them too. And remember...there's more than just Craigslist...
Contest now is very effective in many blog, so for me you must affiliate with bloggers that can be a good help. Many people now are craze in the blog contest and of the site that will advertise for you and guaranteed is the The Contest Blogger Forum
You may want to look into contacting popular video bloggers, and see if you can work out something with one of them. Many bloggers like the idea of being able to bring exclusive contests to their viewers