"Gem-X" by Kaiko (more from this author)
Style: Intellectually challenging
Duh. Another one of those mind-bogglers like Logo.
But again we have a trainer included so don't worry.
After clearing some levels you'll see cute pics. There.

"Girl Simulator"
Style: (more or less) Interactive fiction
As if it was that easy, HAH!
Play the game but don't believe
for a second all girls are that easy.

"Girls they want to have fun" by Brillant Software (more from this author)
Style: Joystick lover
This one's an evergreen for me! Controls are a bit strange
at the beginning. Twist and twirl your stick to move her hand.
Here are scans of the German instruction manual: [1] [2]
Can you beat Telespielator's score of 3271 points?

"Girls They Want To Have Fun II" by Uncle Ben's Soft (more from this author)
Style: Joystick lover
I'll quote Uncle Ben: "This can just be considered a demo and not a
game since you can't gain any virtual points. The pictures were taken
from other Demos/Diashows and improved a little bit plus I added the
vibrator-function which simply consists of two picture setups.."

"Girltest" by TSR (more from this author)
Style: Exotic
Cool, let your loyal C64 choose the right woman for you by evaluating
your answers to certain questions. Of course the answer depends on what
you need her for. ;-) There's also a German version called Maedchentest.

"Girltris" by Reliance (more from this author)
Style: Intellectually challenging

"Glenn or Glenda" by Danzig and Jack the Rapper (more from this author)
Style: (more or less) Interactive fiction

"Goldshaft Deluxe" by Mombasa Joe (more from this author)
Style:
At first you might see nothing dirty except for some
barebreasted chicks in level 3. Well, press 'x' in the menu
screen for Nasty Mode - away with those clothes!