Domain name registrars
A registrar is a firm which registers domain names in the Domain Name System.
See Domain name registrar @ Wikipedia.
WHOIS displays information about a registered domain name.
Various firms offer free WHOIS service.
WHOIS @ Network Solutions
Web host affiliates
See karljones.com for Bluehost affiliate link.
Full disclosure: I earn $65 each time someone clicks through my Bluehost logo and signs up for a web hosting account.