Domain whois tools are important, inorder to check the availability of the domain names you are interested in. Sure you can use the whois search at the registrars like Godaddy, Moniker etc. But they start processing your request when you click the search button.
Here are a couple of tools which search instantaneously once you stop typing the domain name. Use them and you will love them.
2. DD whois
I am happy using them as it saves me a click for each search. Please note sometimes they are not very accurate. But still worth a try.