Earlier this year, Alexa sat down and compiled a list of the top 1,000,000 websites in the world. Listing those sites would be good reading, but looking at a picture of the most popular ones is much cooler.
Nmap have run a script that gathered the 288,945 most popular websites from that list, stuck their icon on a page and then scaled the icons according to the popularity of the site.
The results are far from perfect - Alexa is suspect as a traffic counter, and Nmap admit their own collection efforts aren't 100% effective (Amazon, for example, being tiny) - but for the most part, things look pretty good.
While the site linked below lets you search via URL, go see if you can find Kotaku the hard way!