If you've ever been behind a router/firewall and needed to find out what your IP address is to the outside world, here's a few ways to find that information.
The easiest way is through your web browser:
http://whatismyip.org/
http://www.ipchicken.com/
http://checkip.dyndns.org/
http://myip.dk/
Use which ever is easiest for you.
You can also find it via the shell in Linux, and the Terminal in OSX.
Linux: wget -q -O - checkip.dyndns.org | sed -e 's/[^[:digit:]|.]//g'
OSX: curl www.whatismyip.org