Next to direct SEO traffic, articles submitted to ezinearticles.com are the second biggest traffic generator for me. Of course, you need a whole batch of articles out there to see significant traffic. I remember in the early days it was suggested 100 articles would get you good traffic. Some time later someone mentioned you need at least 250 to see a breakthrough. My guess is that has gone up again. But if you stick at it you will see sustained traffic for years coming from article directories.
if you just need traffic then twitter is the best one u can do almost one tweet in 8 mins and no one will consider you a spammer lets suppose if u got 1k followers then u will get atleast 300 hits in every 8 mins
I believe the premise of you tube is to provide people with a visual of who you are and what you or your product is about! Youtube allows you to reach broader audience , since its the number 3 most popular and visited website on the planet!