As mentioned by the Zend Developer Zone, the Royal Pingdom website has recently posted their look at what the most popular websites on the internet are running. There aren't many surprises in the list, but we'll save those for later. First, a quote:
TechCrunch, FeedBurner, iStockPhoto, YouSendIt, Meebo, Vimeo and Alexaholic. These are some of the most popular websites on the Internet. You have heard about them, you have read about them and you have most likely used or visited at least one of them. But how often have you read about what these websites are actually running on? This article dives into the facts and figures about the underlying hardware and software that keep these sites running smoothly in spite of their massive popularity.
As mentioned, there's no real surprises in the list - Linux still tops out on the server popularity, Apache and MySQL dominate their fields and, according to the numbers, PHP is still on top in the web world. Of course, there are some that these software just won't meet the needs of, so he mentions those too - Meebo with Lighttpd, Alexaholic with IIS and SQL Server, and TechCrunch/FeedBurner with Java and Tomcat.
Check out this PDF report for the full results of their survey.