MarkoH01: Just to make sure that I did not misunderstood you. This thread is not just about games for which you don't have to be online but games that are able to be played without having steam running at all. It sounded a bit as if the "offline" playable thing was the one you were pointing out. Again: I don't want to offend you it's just for my understanding.
josh72718: No offence taken, friend. Without steam? Do you mean like this
http://www.minijuegos.com/juego/sonic-cd (it's in spanish, my mother tongue)
Its simple. Normally steam games require you to have steam running to download AND to run the game. If you run a normal steam game by clicking on the executable without having steam running in the background you will get an error message. So you will have to start steam and log in to your account. However there are some games for which you don't even need to have steam installed after you have downloaded them. You can download the game, store the files wherever you want and then uninstall steam completely.
Long story short: Don't start the steam client, search for the game executable and double click it. If the game is starting and saving/loading you can be pretty sure that it belongs on this list. If you want to be 100% sure try to copy the files of the game to another PC or run them in a virtual PC.