I don't know how much my gmaes are worth for my xbox and PC

A good way to judge the game's value is to look them up on Ebay or Amazon. Right now if you went into a video game store the PC games won't get you anything or very little. Xbox games are not selling for much if you sell them to a video game store. Xbox 360 games are hot now and sell for the most. You can try listing them on Ebay but check the other listings to get a handle on what to charge.

Go to half.com it is sponsored by eBay and it has a lot of video games on it

there is a website where you can swap games for free (goozex.com) you post games you have, they assign it a points value based on what they say it is worth and then you use these points to buy second hand games from other members.

In general if your looking to post your games on craigslist or something like that I usually put $10 for newer games and then $5 or even $2 for old xbox and PC games.