1. If you need traffic now, find a forum related to your niche. Don't find a small forum and hope for a little backlink. Find a gigantic forum. If you need a list, check out: http://www.big-boards.com/. In forums that support it, put your link in your signature in an interesting way (remember, colors are always a plus) and try to sneak it into an original thread with WORTHWHILE AND RELEVANT content.
2. Instead of just forums, find groups. You can use Yahoo Groups (See the "Best of Y! Groups" here: http://advision.webevents.yahoo.com/bestofyahoogroups/) and Google Groups. (You're on your own.) These sites are arranged in such a way that you can instantly enter a keyword for something you're trying ot promote and generate traffic if you have a worthwhile product.
3. Use social media. This includes Youtube, Twitter, Facebook, Myspace and every other site you can think of that you'd find your friends on. All it takes it one re-tweet by a few people, a couple of friends to join a group or a good idea to create an instant viral hit.
4. Disqus. If you've ever commented on a Disqus blog, you've used it before. Find Disqus-enabled blogs and post WORTHWHILE comments. If your comments get picked up by subscribers, then you will make a lot of traffic flow your way.
5. Use one of the aforementioned methods to begin with, but make your site "invite only." Examples of this include Demonoid and Likaholix. If you offer a sense of exclusiveness, you can generate a large interest and kindly "push" people into telling their friends about your site.
That's absolutely it. I'll admit that the fifth point is rather skimpy as it isn't a technique all on it's own, but I thought it was worth posting. Keep in mind that every single one of these points rely upon the fact that you have something either worthwhile or interesting to say. Don't try spamming for viagra online with these techniques, because you'll only be hurting yourself. (Unless, of course, you find an eretile dysfunction forum. Then by all means, cure... Er, I'll quit before I get too far off topic.