The Secret of Monkey Island -- First game I ever bought, after that I was hooked on adventure games and everything Lucas Arts.
Thief II: The Metal Age -- Played this for hours, then replayed not killing, then again without being seen and not killing
Epic Pinball -- Kept the family occupied for ages. rediscovered in 2012 and still playing it
Star Wars: X-Wing (Collector's CD-ROM) -- I played & replayed some missions for weeks until I cracked them. Still haven't got the hang of flying a B Wing
Thief: Deadly Shadows -- More of the city but it still seemed small. Excellent game though.
Thief: The Dark Project -- Got the Gold version. One of the few games I have played three times
Sam & Max Hit the Road -- A classic without which I'd have never known there was an official 'worlds largest rubber band ball', or was that twine?