1: Command & Conquer 8) and the rest of the 'Westwood' productions. (Not EA :evil: )
The others are the most memorable of each genre and are in no particular order.
Malkari - Excellent ship customisation and tech tree enabling very long games and limitless replay value.
Tachyon: the Fringe - First space combat simulation I played, I've not been able to resist the genre since. Plus Bruce Campbell does the voice excellently.
Battle Realms: Winter of the wolf - Very enjoyable Japan based RTS that wasn't afraid to add humour and character development into the storyline.
Diablo 2 - Good array of classes and skills improves the game over the previous and the random map generation gave it the replay value that made it stand out above the rest.
UFO:Enemy Unknown - First of the X-com series and herald of a few recent clones, making use of new graphics. Another of my favourite genres.
Worms 2 - Best party game in the world. Even my family likes it's silly fun.
Halo 2 - The focus of much fun and fragging during my college years.
The final two are memorable, but for the wrong reasons.
Neverwinter Nights - Source of the worst ever visit online, seems to be full of complete assholes.
X2: The threat - In my extended gaming history, this is the worst designed game I've ever had the misfortune to play. At least I wasn't the one who bought it.