Allow new members to put in another player's username in a box labeled "referal" when they sign up.
I have told people at school "try Conquerclub, my username on there is 'Mr_Adams'" but then I don't get them on the referal page, because they google searched for CC when they got on thier computer, and didn't use the link I sent them.
If I'm playing a game of poker online,or something like that, this would make it much easier to refer players, than to have to type the whole code into the text box and then have them type it all into thier address bar...