Really anything by Sierra or Lucasarts you can't go wrong— some are more frustrating than others though. I'd recommend The Secret of Monkey Island 1 and 2, Indiana Jones and the Fate of Atlantis, Conquests of the Longbow, Space Quest 4 and 5, Gabriel Knight: Sins of the Fathers, and Quest for Glory 1 (EGA or VGA version, whichever you prefer). There's a ton more out there that are all great, but it depends on your tolerance for bullshit.
Then of course you've got your Apogee platformers like Commander Keen and Biomenace, and the classic FPS games: Doom 1 and 2, Duke Nukem 3D, Blood, Redneck Rampage, Quake, Heretic, Hexen...
Other games I've always loved are Lemmings (there's 50 trillion versions of it), Myst, Riven, Warcraft 2, and a bit of Civilization.
Getting into the Windows 95/98 era (not sure how many of these you'll be able to run, but suggestions anyway...), the RTS games like Caesar 3, Age of Empires 2, and Heroes of Might and Magic 3 are all phenomenal. Half Life, Worms 2/Armageddon, Baldurs Gate, Planescape Torment, Thief, Deus Ex, and System Shock 1 and 2.
Christ, that's just a few of my favorites. I must warn you that some of them are a little more janky than others... Thief took me many years of playthroughs to finish, and I've never finished Baldur's Gate or Deus Ex... That said people talk extremely highly of them and I did find them quite enjoyable so they're worth a shot.