If you click the buy button the dialog will show which games come with what. In this case Four Horsemen and Emily is Away Too. If any of the other developers add Steam keys to their page you'll get them too, but we can't make any guarantees about that. You can always try asking them!
To add to Leafo's answer, you can check at the bottom of a game's page whether or not it comes with a key. It'll say something like, "In order to download this game you must purchase it at or above the minimum price of $0.00 USD. Your purchase comes with a Steam key."
