I like this tool
http://www.networksolutions.com/whois/index.jsp
Also here you can find the cache history of a domain (very useful)
http://www.who.is/whois/cache.com/
- - - Updated - - -
Other links to check domains:
http://spyonweb.com/
http://www.spyfu.com/
http://www.domaincrawler.com/adspy/