A couple of tidbits:
jhobin is right with tau not being overpowered whatsoever....they are really a 3rd/4th edition playable army.
As for unbeatable lists, yes, they exist. I should clarify: it exists. Imperial Guard. Broken codex? yes. I would cheerfully defend this against any and all army lists or conflicting viewpoints if anybody would like to argue it (start a new thread or PM me or something, not here).
And yes, 1 force org per customer per standard 40k game.
what the hell, imma take the imitative and post the unbeatable IG list. This proves that money, indeed, can buy you victory. Isn't that the GW motto?