SSL Alerts - Free service to send SSL certificate expiration alerts
NakedSSL - Hassle-free SSL clothes for your naked domains.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Kilo SSL - Automatic SSL management solution for SaaS providers
Secure My Website - A pain-free service to add SSL to your site, for non-geeks
haveibeenexpired - No more expired SSL certificates