I say: This one's been in my toolbox for at least 5 years and even though I don't webmaster for anyone else anymore, I still use this whenever I want to look up domain name availability.
They say: "If you've ever registered a domain name, or even considered it, you've probably discovered what a hassle it is using the web-based interfaces to the old UNIX command, whois. Wouldn't it be cool if there was a more hip, GUI solution? I thought so, and here it is...
AnalogX WhoIs is a GUI application that goes out on the net and looks up domain registration information. How is this useful? Well, there's several uses for this particular tool; first and foremost is identifying whether or not a domain has already been registered. WhoIs also will let you enter already registered domains and return the administration/owner contact information, in case you want to contact the people directly.
Of course, if that was all it did, then it wouldn't be much of an improvement... But there's more, you can also automatically launch your web browser and have it go to the page you just did a request on! Still not enough? You can even enter in keywords and have it scan for different domain name combinations - then generate HTML reports from the results! What about people who don't live in the USA, and want something other than a .com/.net/.org? No problem - WhoIs ULTRA supports ALL top level domains (TLD's), and you can quickly and easily add your own to the list! So if you're serious about domain registration, or even just curious, check this out!"