-Battle of Britain: really, really old flight combat sim , from Lucasarts I think. Could have 16 aircrafts in the air at any time and had a mission builder, a revolution back then
-Air War over Europe(think it was called that): Slightly newer than BoB, more aircrafts in the air and a great dynamic campaign with some historical missions and heroes included. Fun to dogfight aces like Josef Priller, Hermann Graf etc in campaign.
Spent an awful lot of time on these two...

Others...
-Championship Manager
-Tie Fighter
-Master of orion II
-Panzer General
-Shogun/MTW of course...