Humble Bundles typically last a while, but this 're-bundle' of Codemasters games is a 24 hour only thing. So if you want to pick up a handful of games — including Overlord and Overlord II, plus games like DiRT 3, DiRT Showdown and a bunch of Operation Flashpoint games — you should probably get a shift on.
At time of writing there are about 19 hours left on the sale.
The full list of games available is as follows:
Overlord Overlord: Raising Hell DLC Operation Flashpoint: Red River Operation Flashpoint: Dragon Rising Rise of the Argonauts
As always, you can pay what you want, but pay more than the average (currently $6) and you also get these games:
DiRT Showdown DiRT 3 Overlord II
Head to the Humble Bundle site for more info.