I downloaded Torchlight on my laptop. Really great game.
Terraria. It's like Minecraft, only a 2D side-stroller and it's more adventure based than building based.
There's also Crayon Physics Deluxe, it's packed with the Humble Indie Bundle and it's pretty fun

I have both Torchlight and Terraria... haven't tried them on my netbook though.
Terraria gets old really fast once you've maxed out your character :/
Doom.
Day of the Tentacle, or any other DOS point and click game.
ooh I'm definitely buying DOOM
Beneath a Steel Sky (1994)

If a computer fails to run it, it doesn't deserve to exist.
I'll check it out (it's on GOG right?)
I wonder if Dwarf Fortress would destroy that.
no! I am not going anywhere near that thing again. It is evil! EVIL I TELL YOU!