domaintools.com . Run a domain WhoIs on the site to give you the host an owner. Running a standard WhoIs on the parent company should give you all listed domains. For an additional $20, you can also get all domains hosted by the host.
Is this what you're looking for?
LOLLL $20?? LOOOLLLL use simple UNIX tools to enumerate that information:
wget "whatever.com" && cat index.html | grep "href=" | cut -d "/" -f 3 (should be good)
or try the (FREE) listurls python script in Back|Track 3
or search google like this "site:<victim>.com"
Do "whois <victim>.com from the command line of the (FREE) backtrack CD
The Whois result will usually include the whole network range which belongs to the organization.
type "nslookup" from the cmd line and then at the ">" prompt test different services/types like
"type=mx" (mail servers) or "type=ns" etc
you could also write a bash script that reads a file line by line, (full of words), and stick that variable like so:
$variable.<victim>.com and it could simply do wget and stream edit the output with "grep, sed awk" to show you only live subdomains. etc.
try using the host command to enumerate data about the DNS servers used as well.
hope that helps.
<3 Trev.