WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
HostedScan.com - Online vulnerability scanner for servers, networks, and web applications.
Whoisology - Connected database of whois records and whois history
HackerTarget.com - Security Vulnerability Scanning based on Open Source Tools.
JSON WHOIS API - Parsed domain WHOIS data from any WHOIS server via RESTful API with metered pay as you pricing.
Acunetix - Audit your website security and web applications for SQL injection, Cross site scripting and other...