Hey you asked my top 5
Anyway, I also forgot to mention one of my fave games of all time, I dunno if you remember it, centurion, all about roman legions and taking over the known world (brilliant). For all those who fancy a touch of the oldies, most of these games can be downloaded at the following location...
http://www.theunderdogs.org/
also, yes I remember X-com, terror from the deep. It never got the credit it deserved, remember the way your men died, screaming and falling down, class. I real hated that floating brain that killed my men and then turned them into another floating brain.... uurrrggghhhh...