TrueIP - TrueIP is a small program that runs in the system tray, monitoring your IP address(es).
Whoisology - Connected database of whois records and whois history
My Public IP - My Public IP is a utility to let you know through which internet IP the world see you.
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
IP-Toolbox.com - IP-Toolbox.com is the best site for quick and easy viewing of your public IP address and other related information.
JSON WHOIS API - Parsed domain WHOIS data from any WHOIS server via RESTful API with metered pay as you pricing.