I have a few.

• Doom 2
• MyHouse.WAD (which I consider completely separate from Doom 2 in this sort of discussion.)
• Dr. Langoskov, the Tiger, and the Terribly Cursed Emerald
• Curse of Monkey Island, original trilogy
• Strong Bad’s Cool Games for Attractive People (and pirates now that you can’t download it legal-wise no more, but I repeat myself)
• Galaga
• Hotline Miami
• Helltaker
• Terraria (Googling is allowed after the first six hours)