Zork = text-based adventure. 1980s or so I think, but you can find a free download in several places now. Positively lovely.
NetHack = t3h awesome. Another 1980s or so game. Sort of textbased, but more like the symbols and letters represent things on the screen. Like the @. The @ is you and can represent shop keepers. | is a wall, + is a door and so on. There's also a graphic version, but you lose the true feeling to the game if you go that route. Available free online for download.
Grim Fandango was AWEESOME. Does anyone remember that claymation game with the duck guy? It was "neverworld" or something like that. It was a puzzle game. Great one, too. From the creators of Catscratch (which is a great show).
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Delicious Turkeys of Fury, Obesity Man!!!!!! THE WEBSITE IS ON FIRE!!!!!!!!!!