ARIN's WHOIS service provides a mechanism for finding contact and registration information for resources registered with ARIN. ARIN's database contains IP addresses, autonomous system (AS) numbers, organizations or customers that are associated with these resources, and related Points of Contact (POCs).
For some reason I always forget how to lookup the owner of a netblock. From the command line:
whois -h whois.arin.net W.X.Y.Z