Text adventures were mentioned earlier. I don't remember Adventure but I did try a few that were put out by Infocom. I didn't do too well at those. It might be interesting to try them again, though. Are any still available that work on today's computers?
I'm still trying to get my hands on Portal Jon. It's been driving me insane, I'm trying to get it for PS3 in The Orange Box but they sell it so cheaply that whenever they get some in it's gone before I can get my hands on it. I'm considering just biting the bullet and downloading it from their site for PC. The only problem is that I am the opposite to you, if I'm gaming I need a controller in my hand. The only games I feel comfortable playing on PC with a mouse are RTS ones (Age of Empires etc ). I think if I download Portal it will take me a long time to get used to using a mouse for a first person game.