One website I found extremely useful when initially learning regex was http://regexr.com. It's got a great pattern builder, and hovering over each component explains what its actually doing.
I don't understand why businesses use use private WHOIS services. Surely if you're a business you'll have public contact information? I was once tasked with trying to get in touch with a company who's domain name had expired, but with no website (read: contact page) or real email address in the WHOIS I had to give up.
