Is there a service that will identify where a site is hosted (presumably by IP)?
tracert www.sitename.com
is probably your best bet. The last entry or two should give you your best hint. Otherwise, the whois entry may be a good indicator as well, especially if they are using a hosting provider for DNS.
EDIT: Its traceroute not tracert on linux machines.
Just do a whois search on the IP.
http://samspade.org/whois/ is a free utility for telling you who owns an IP address or domain name. If this is a server farm hosting multiple servers, then it will likely be registered to the hosting company.
Domaintools can usually give you some pretty good information, under the "Server Data" and using the "Reverse IP" tool (though you have to pay to get full results from that one).
http://whois.domaintools.com/websitename.com
just put the website name in instead of websitename.com.
try here
Who-hosts is an online free service that can tell you which is the company that hosts the provided URL. No need for registrations or w/e
This isn't exactly what the question asked for, but you might find it useful to know that Netcraft provides some pretty neat information about the uptime, web-server software, and ISP used to host websites as well.