We've added the most popular and most valuable PC/DOS games to PriceCharting.
You can add these to your collection and find the value for them too.
Unlike other consoles, we will not aim for a complete game list with PC games. There are too many junk/shovelware/worthless games to keep track of. If you see a popular or valuable game missing please add those, but don't add "Shovelware 100 in 1 Game Compilation" discs. If the game was available at Office Depot on the impulse rack by candy bars, it probably isn't worth adding :)
Also, we are only tracking games, not all Windows software so you won't see prices for Office 2009 or Lotus Notes.
Please give us any feedback on the list and anything else about PC game collecting you want to talk about.