CloudFlare - Cloudflare is a global network designed to make everything you connect to the Internet secure, private, fast, and reliable.
BrandSSL - On demand SSL for SaaS
Google Project Shield - Google's DDoS protection service
CertSimple - EV SSL certificates delivered in hours, not days
SSL Alerts - Free service to send SSL certificate expiration alerts
NakedSSL - Hassle-free SSL clothes for your naked domains.