I'm not sure it's something that anyone has really tracked and having done a spot of googling, I couldn't find anything meaningful either.
Without any figures it's impossible to say for sure, but I'd guess PHP and ASP.NET are probably the 2 most commonly used techs at the moment.
Also, even though classic ASP 3.0 might be considered "dead" due to it's age, I certainly see quite a few major sites, including my own banks website using asp, and these sites have certainly been built a long time since .NET came on the scene in about 2000/2001?
And to add to the server side tech list, there's also Coldfusion from Adobe (formelry Macromedia), although the number of sites I've ever visited that I've noticed using it I could count on the fingers of 1 hand.