Name: Seeking Alpha
Website: www.seekingalpha.com
What it does: Seeking Alpha's roots are in investment opinion, aggregating analysis from investing blogs. The site has added its own short-form news stream, as well as stock and market data, making it a full-blown investing portal.
While many bloggers contribute their content to SA freely, the company does offer them payment via its premium program (details here).
Particular strengths: Check out Seeking Alpha's ETF content, some of the best online. Seeking Alpha's alerts system is also really valuable -- you can get real-time emails with breaking opinion on stocks in your portfolio or watchlist. Also, if you're looking for good ideas, check out SA's long and short ideas.
How popular is it: On a monthly basis, Seeking Alpha reaches 5.3 million global users, serving up 75M pageviews. (Source)