I swear there used to be a site with a database of subdomain names. Like you type in the main domain name, for example: domain.com, and it serves out a list of recorded or known subdomains, such as mail.domain.com, serverx.domain.com etc. I've been searching google for the past hour and played around with nslookup, but I'm stumped.

Anyone wanna shed some light on this one for me and whoever else may be looking for this type of information?