The recent Weekly Humble Bundle contains several good games developed by Bohemia Interactive. If you pay at least $1, you will get Arma 2, Arma Gold Edition, Take On Helicopter Bundle, UFO: Afterlight, Alpha Prime, Fish Fillets 2 and an additional game that they will add later on.
You can unlock more games if you pay the average price of all users. This would add Arma Tactics, Arma 2: Operation Arrowhead, Arma 2: Private Military Company and the Arma 2 DayZ mod which is included although it is free on Steam anyway. Also in this tier you will get one further game that they announce later.
Then you have the option to pay $20 and you would get early access to Take On Mars and another secret game that is not announced yet. Last option is to pay $100 to get the whole Bohemia Interactive Collection, this would unlock all of their games on your Steam account.
To be honest, the $1 tier is already a good deal because Arma 2 is a very good game that I played quite a lot in the past, I’d suggest this game. But it would make sense to pay the average price to unlock tier 2, because the Arma 2 expansions are really quite good as well. This is definitely a bundle I would suggest to get.