CloudFlare - Cloudflare is a global network designed to make everything you connect to the Internet secure, private, fast, and reliable.
Sucuri - Website Protection, Malware Removal, and Blacklist Prevention
Google Project Shield - Google's DDoS protection service
Amazon CloudFront - Amazon CloudFront is a content delivery web service.
SSL Alerts - Free service to send SSL certificate expiration alerts
Qloaked - Painless customer SSL for SaaS businesses