I did a website for a business about a year ago, and now the owner is selling it and wants to sell the website along with it. The only problem is, he wants to know who my server was, but I can't remember who I went through. Is there any way to easily find out this information without having to call every single ISP listed on the internet?? Thanks.

What is the domain address? You can do a whois search at www.whois.sc and get some information. Usually the nameservers will have the hosts name.