CloudFlare - Cloudflare is a global network designed to make everything you connect to the Internet secure, private, fast, and reliable.
AWS WAF - AWS WAF is a web application firewall that helps protect your web applications from common web exploits.
NakedSSL - Hassle-free SSL clothes for your naked domains.
ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.
Secure My Website - A pain-free service to add SSL to your site, for non-geeks
Barracuda Web Application Firewall - Barracuda Web Application Firewall offers security and DDoS protection against automated & targeted attacks.