How it works
1) Register http://signup.leagueoflegends.com/?ref=4f5b2e39f2bb6803743280 the link will change from time to time, as it can become invalid as Riot doesn't like people having it, This 100% works during Varus's patch and i'll update it for upcoming patches
2) Play Until you reach level 5 or more (May need level 6 so Riot's server can verify you got to level 5) (This step is vital or Riot will think you are an account spammer and delete your account)
3) Log out of League of Legends
4) Restart Your Computer (So that any files that may have LoL open get closed) (Or if you don't want to restart you could log into the League of Legends homepage to verify you are level five)
5) Relogg (Log in and it should work)
6) You should have enough RP to buy what ever you want and possibly the champions (If you don't get the champions you can just buy them now)
Note once you sign up via the link, you have to use the account you signed up with via the link to get to level 5 or it won't work