openssl.exe s_client -connect www.mysite.com:443

which will use a generic SSL/TLS client to connect to your site and give you a ton of diagnostic info.  You can see your entire SSL cert chain, the SSL handshake, SSL session info, etc.  Here’s a full list of switches you can use with it:  http://www.openssl.org/docs/apps/s_client.html

And here’s a great online tool to graphically verify your SSL chain is intact:  http://www.sslshopper.com/ssl-checker.html

A quick way to troubleshoot SSL chain issues using OpenSSL is a post from: JasonSamuel.com

More of my posts you might like:

1. SSL certificate chains explained