Online Domain Research Tools | Whois

Whois lookups are a handy and useful way to find out who owns a domain and when it expires. Sometimes it's easier to do a whois lookup on a domain YOU own to see when it expires than it is to go back and check your (or your organizations) records. These days the online domain lookup tools have started expanding the kind of information they give to include such as the history of the domain, other domains owned by the contact, information on the server, the registrar, the DMOZ status, SEO information, related sites, etc. (Dizzying.)

One tool that I've made quite a bit of use of is whois.sc they have recently moved to whois.domaintools.com

The array of tools that they give in one place is a bit overwhelming but can be useful if you're looking to buy a new domain as well. The tools they have could give you an idea if the domain has been in use previously, if it's been blacklisted or the like. (You can also setup free monitors on domains.)