I have spent a lot of time marketing my site and getting backlinks from popular design based websites like DesignFloat, DesignBump, Webmasterclip, Web Designer Depot... but these are specific for the web/graphic design niche. If you run any type of analytics or tracking software, what are your top referring sites? I only ask because I am looking to broaden where I market, and I am wondering where I should spend my time (Digg, Delicious, Squidoo...)
YouTube and Yahoo! Answers are two of my biggest referrers, and 100% of that traffic is organic. I'm sure with a bit of effort either can be made to produce tons of traffic.
I had not considered Y! Answers, but that's actually a very good idea. I hear a lot of success stories about advertising with them, so I may give them a try.
Recently it's Bing. Normally it's wemaster forums like DP or the odd blog that sends a fair few visitors my way.