Google sends more traffic to WikiPedia than any other site, according to Hitwise. I've noticed that WikiPedia has top rankings now for more and more searches. Since they've doubled their article count over the past year, to 1.5M english articles, their search footprint has expanded. This trend will only continue.
This is also exactly the kind of destination content that Google loves. The articles are excellent quality, and WikiPedia is entirely non-commercial, so Google can feel good about having them rank at the top of the organic listings. Any algorithmic changes Google makes in the future are likely to preserve and reinforce this effect.
Google accounts for nearly 50% of their inbound traffic. But "wikipedia" is their top inbound search term, so people are seeking the brand out directly, as Steve Rubel notes a year ago.
The full list of top-10 Google downstream sites is:
This list doesn't distinguish between paid and non-paid listings, but clearly WikiPedia isn't buying adwords so 100% of their juice is organic. Given how often I see About.com come up in the results I'm surprised to not see them in this list.
It will be interesting to see whether Jimmy Wales can replicate this success with Wikia, the VC-backed commercial twin to WikiPedia. 100% revshare, wow -- I don't fully get the model yet but he's clearly got a bold plan up his sleeve.
More Hitwise coolness from SEOmoz.