Forward port 80 to your server, and typing in the WAN in a browser (from outsiede the LAN) will be directed to the server transparently. This is assuming that your ISP does not block port 80, of course. If that is the case, you will have to use a different port for your server.
You can uses a service like
http://www.no-ip.com for dynamic DNS redirection to avoid registering a domain. It is how the SE4 tracker works:
http://kazharii.no-ip.com:6969