Here is a handy little tool we developed:
http://www.CanYouSeeMe.org

This tool will check for open ports and see if there are any services responding on that port.  It comes in handy when troubleshooting your network.  Specifically it helps in checking to see if your ISP blocks certain ports such as HTTP port 80 and SMTP port 25 (commonly blocked by major broadband residential ISPs).

Additionally if those ports are blocked, No-IP has a solution that will get around this block. Users with ISPs that block the standard http port can use the port 80 redirect feature available to all users.  This can be found in the member section why managing your host.    No-IP also offers Mail Reflector and Alternate-port SMTP service for those with ISPs that block inbound and outbound SMTP port 25 respectively.

Keep in mind when using this tool you will need to open up the canyouseeme.org website from the same WAN IP address that you wish to check for open ports.