StarCraft 2 has a coop mode which is a ton of fun imo, around 18 different commanders which range from “small spin on an existing race” to “essentially 5 hero characters and no units”. You play with a friend or queue up with a random other player and play from a pool of amped up campaign missions.

No other game comes to mind, but Stormgate also promises a 3vAI mode, which will be playable next week on Steam Next Fest.

To me this looks like WC3 units using the SC2 engine, on a Dawn of War map, which I all like.