The Humble Bundle weekly sale is an offering from Codemasters. Seven games and an expansion are available from the DiRT, Overlord and Operation Flashpoint franchises.
You can donate your payment to Special Effect, a charity which helps people with disabilities play video games. Special Effect uses modified controllers and eye-control devices that allow people to enjoy games regardless of their physical ability.
"We're not just doing it for fun. By levelling the playing field, we're bringing families and friends together and having a profoundly positive impact on therapy, confidence and rehabilitation."
For $1 or more you can grab Overlord, Overlord Raising Hell (Expansion Pack), Operation Flashpoint: Red River, Operation Flashpoint: Dragon Rising and Rise of the Argonauts.
Overlord's actually a pretty good laugh even if it's a bit limited, giving you control over a bunch of absurd imps as you try to cause havok throughout a fantasy kingdom. Operation Flashpoint is a nifty military shooter/sim, and I used to play Dragon Rising to death before I got hooked on Arma.
Rise of the Argonauts is just not very good. But it does butcher Greek mythology. Screw those ancient myths.
Spend $6 or more and you can also pick up DiRT Showdown, DiRT 3 and Overlord II.
All of this would cost you about $100/£70 if you picked them up on Steam.