Yep, any classic Lucas Arts games will keep you busy for a while.
Also don't forget the old Sierra games, like King's Quest, Space Quest, Quest for Glory, Gabriel Knight, etc.
Dynamix made some neat adventure games too - Gobliiins, Gobliins 2, and Goblins 3. (Gobliins 2 is probably the best, but they all rawk).
If you have Windows installed on this machine, dig up a copy of Sierra's Woodruff and the Schnibble of Azimuth.
Be sure to pay your respects to X-COM: UFO Defense and X-COM: Terror From The Deep. The gods of old-school gaming will know if you don't.
If you like action games, try ABUSE. That game was way ahead of its time. Also check out Blackthorn.
Some good puzzle games:
The Incredible Machine
Laser Lights
Bolo - oh man, if you find this game somewhere, PLEASE PM ME - it was on a demo disc some years ago, but I've never ever seen it again. Its a Windows game, and involved using the mouse to jerk around a black sphere on a chain (connected to the mouse), do solve puzzles and such.
Aah memories...