[TCattitude]

ELO? This: http://en.wikipedia.org/wiki/Elo_rating_system

I play in a FPS community some times (when work and family allows :P ) and they have a Ladder (and old one: medal of honor). They use a ladder system from mygamingladder dot com.
They used to have that kind of scoring, by points, years ago. The problem was some clans was always playing with newbie clans, or even "clon"-clans, and they was just sum points and keep in the top of the ladder 4 ever. So they change the rating/scoring (don't know if was their idea or a change in mygamingladder).
When two clans play, the loser report the loss, and when the winner confirm the victory, the points are given (when loser not want to report, they can go to the forums, post screenshots of the matchs and scores, and reclaim their victory anyways, with a penalty for the loser). If the winner was the most higher rated clan, then nothing happen, the higher clan just wins another "victory"; and they sum the number of victories in a row to give you your best run of all the time. But if the lowest clan wins the match they go up in the ranking by the half of the point that was separating them from the higher loser clan. So, A and B play; A is in position 10 in the ladder, B is in position 20 in the ladder. B wins. A just stay in position 10. B go up to position 15, the middle between 10 and 20.
That way, whatever clan can climb in the ladder, and are no points, just positions in the ladder, and no clan can climb to the top and get far away from the others accumulating too much points.