A useful script that discovers the expiry date for a given certificate: ssl-expiry-date. At some point I slightly modified this script to read a Bind DNS zone file and check each
Arecord for SSL Expiry, for the purpose of discovering which subdomains were using a wildcard SSL certificate. I should publish that somewhere some day...A very clear explanation of SSL encryption, not specific to OpenSSL, but it uses OpenSSL for all its examples: Secure your website with SSL encryption.