Andreas' answer above was helpful in solving my problem of how to test artisan on port 80. Port 80 can be specified like the other port numbers, but regular users do not have permissions to run anything on that port.
Drop a little common sense on there and you end up with this for Linux:
sudo php artisan serve --port=80
This will allow you to test on localhost without specifying the port in your browser. You can also use this to set up a temporary demo, as I have done.
Keep in mind, however, that PHP's built in server is not designed for production. Use nginx/Apache for production.