I figured you'd all be interested in this topic, seeing as that is what this site is about after all. Using a variety of sources including reddit, the Steam Community Discussions boards, PCCouchCOOP, and Co-Optimus itself, I created a list for the PCGamingWiki in an attempt to make a well-sourced, easily navigatable and updateable list of PC games which support local/couch co-op play. Said list can be found here.
I found that there was no real quality source of information for PC games which was easy to use but also comprehensive. While Co-Optimus is a fantastic site with a large community, I found that, at least in regards to PC, many games were lacking articles, images, and the like. My goal with this list was to create a resource which included every co-op game available for PC I could possibly find. Due to the friction of creating an article on Co-Optimus, I chose instead add it to a community I already had experience in. That's a general fault of all crowd-sourced projects, not yours by any means. I really do hope that my list helps users here to fill out more of the PC games which are, at present, missing articles despite featuring co-op play. I am by no means not trying to take hits at this community, but rather attempting to explain my logic in creating the list for another site rather than expanding the large collection of content already found here.
As for why I chose to limit the list to local/couch multiplayer, rather than including online or LAN cooperative/versus play, I felt that this specifically was a segment of co-op which was severely lacking on PC. It was a shame that, despite Valve's push towards SteamOS, Big Picture, and Steam Machines, developers had thus far failed to bring support for local multiplayer to the PC platform. Many games which included split-screen on consoles failed to retain that feature in their PC counterparts. I felt that this list was something that could be beneficial to a huge number of people in the near future when Steam Machines are released as full consumer products.
On my own I managed to create a decent list of a few dozen games, but without the help of a huge community of PC gamers I don't think I would have been able to make it much farther than that. I am deeply appreciative of not only the content I managed to find through this site, but similar sites and other gaming communities such as reddit's /r/games. I think the project has been a great success thus far. I don't plan on stopping it any time soon and would appreciate any suggestions or contributions you would like to give. Similarly, I would love if those of you more experienced in contributing to Co-Optimus could add articles for the games I have in my list. I'm still focused on making sure my list is comprehensive so I won't start contributing to Co-Optimus just yet, but I'd very much like to in the near future.
Once again the list is available here. Thank you for reading and providing such fantastic information through your contributions to this site. Happy gaming.