Which sites do you use? Check the official list here. (according to eBizMBA Rank)
1. Google – 900,000,000 – Estimated Unique Monthly Visitors
2. Facebook – 700,000,000 – Estimated Unique Monthly Visitors
3. Yahoo! – 500,000,000 – Estimated Unique Monthly Visitors
4. YouTube – 450,000,000 – Estimated Unique Monthly Visitors
5. Wikipedia – 350,000,000 – Estimated Unique Monthly Visitors
6. msn – 325,000,000 – Estimated Unique Monthly Visitors
7. Amazon – 250,000,000 – Estimated Unique Monthly Visitors
8. ebay – 210,000,000 – Estimated Unique Monthly Visitors
9. Twitter – 200,000,000 – Estimated Unique Monthly Visitors
10. Bing – 165,000,000 – Estimated Unique Monthly Visitors