***SPOILER***

Hmm, perfect example: The Grox from Spore.

There is no way to beat them. They are in the space stage. Seriously, you can't beat them. You can travel from space system to space system, but there are a couple systems you can't get to, but they can get to you, and since you can't get to them, they will continue to build up money and just send waves after waves of dudes after you. They have over 1000 star systems as well, which is retarded.

I am guessing they made these guys impossible to beat so that they could release something cool in an expansion pack (we all know that Maxis loves their expansion packs). Even still, why put the main bad guys in the game and make them unbeatable!