It appears that Sony is currently testing game rentals on the PlayStation Store.
MP1st discovered the following game page on Sony's online marketplace, providing gamers with the option to choose from a number of different rental options. Note: The "Free" pricing options are obviously only there for testing purposes and will certainly be filled with dollar amounts when the service launches.
In addition to this, a post over on NeoGAF adds credence to the fact that this is all tied to PlayStation Now, Sony's cloud-based streaming service.
PlayStation Now's pricing was supposedly leaked a few days ago. With Sony's streaming service expected to launch in just a matter of months, there's a good chance we'll be hearing a lot more about the future of PSN game rentals very soon.