Cloud Cultivator has a great feature which identifies and alerts you to SSL certificate expiry.
By default, Cloud Cultivator will alert you if your site will expire in the next 30 days. If you want to change that default, you can choose any expiry between 8 to 180 days in the future. Cloud Cultivator will alert you about your expiring certificates every Tuesday. As you can see from this example, if I happen to set the certificate expiry to 79 days, I have a domain (this one) which is expiring in 58 days, so I will be alerted to this every Tuesday. You can also list your sites according to expiry date, and drill down into the site configuration from the Site List menu. Check it out here: https://cloudcultivator.com