The top google results for others were actually pretty crappy. Works fine for the really common tlds but that's about it. What does everyone else use?
To install it on Ubuntu:
apt-get install whois
or on CentOS:
yum -y install jwhois
On Windows you can download it from here: http://technet.microsoft.com/en-us/sysinternals/bb897435.asp...
To use it, simply type on the command prompt:
whois domainname.com
I find this approach much faster and easier than using a website that essentially does the same thing. Not to mention that there were rumours a few years ago that some of those websites are capturing what you're searching for and register the most interesting domain names hoping they will sell them back to you.
I hope this helps.
Cheers,
Liviu