i wonder that really, mine is
1. Stronghold Crusader
2. Red Alert 2
which is not really old but i played those for over 10 years. And these were my mega old fav games:
1. Biomenace 1&2&3
2. Liero (the best shooter game ever!)
3. Prehistorik
4. Supaplex (one of the hardest and funniest puzzle games)
5. Volfied i guess most people know this
6. Prince of Persia 2D which is mega with 1 hour time limit and 12 levels
7. Wolfenstein 3D maybe the first 3D shooter game uber fun in my childhood
8. Doom all people know this
9. Duke nukem 2D platform game
10. Dyna Blaster - same as bomberman
And some from atari
1. 1943 one of the hardest games in atari
2. Jackal
3. Tank1990 everyone know this
also known as Battle City
Also a suggestion of flash games after all:
Desktop Tower Defense 1.5, Pro, Desktop Defender(via facebook)
And the uber gemcraft best flash game ever! 3 games and 4th is coming, chapter 1, then 0 then lost chapter, and chapter 2- in development.
Share some of yours old games=old days always nice to remember