The Steam Thanksgiving Sale of 2012 is set to start later today, November 21, according to a developer, and now some of the special items that will be sold during the event have been leaked, including Collections for Mass Effect, Painkiller, Orcs Must Die, or Stronghold.

Valve is notoriously secretive about its sales sprees on Steam, but it seems that the upcoming Thanksgiving one has been leaked ahead of time by a couple of game developers who advertised some of the upcoming discounts before the start of the Thanksgiving sale.

Now, the CDR Database, which is a website that scans the various updates and new entries added to Steam, has posted some rather interesting upcoming items.

Among them are things like a Mass Effect Collection, a Painkiller Complete Pack, an Orcs Must Die Franchise Pack, a Stronghold Complete Pack, a Double Fine Bundle, or a Max Payne 3 Collection.

Do take these listings with a grain of salt, however, as Valve does add a variety of new things to Steam but it doesn’t really mean that it will actually put them on the store.