I don't think it's one of the most known languages, but it is in quite a lot of websites. Although, it may not be very known, I don't think it's dead, because Microsoft probably wouldn't be wasting resources to keep creating their Visual Web Designer (ASP, I think, couldn't really use it) if the language were dead.
Here are some commonly used websites that use asp:
hotmail.com - Microsoft email
asp.net - Wonder what that is
microsoft.com - and all their subdomains (e.g. msdn, msn, etc.)
Well, those are the ones I had enough effort to find, but there are plenty more (not just used by microsoft though). Whenever you're browsing around the internet just look up to the address bar and check to see if the url ends with .aspx, and you'll have found another site.