As well as Loquax there are other competition & freebies sites that you can use to spread the word. There are competition forums and newsgroups too.
However, don't just target obvious competition entries! Create an eye-catching image-link on your front page, and mail out a newsletter (if you have one!) telling your regular users about the competition.
Use newsgroups, forum and social networks to promote your competition too, but be careful not to spam. Be up front and honest and always ask permission of the forum owner before posting a link to your site.
You could also use Adword Campaigns or an affiliate program to attract visitors.
Remember a competition is part of your site's marketing strategy - so promote, then promote, then promote again!
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