All three seats in a '97 Ford Escort (driver, passenger, backseat). Back of a mid-90s dodge minivan, and back of a gf's parent's full size van (chevy I think, but it's been ages).
All of this was long ago and far away - been over 5 years since the last time in a car.

1973 Grand Torino Sport.......(watch for the theme here)

1976 Grand Torino Elite (new that year)........My mom caught us in that one too! Arrgggggggg!

1985 Dodge Ram Charger

1985 Chevy Camaro

1995 Chevy Camaro

1999 Dodge Durango (if waxin his carrot is considered sex amoungst anyone aside from Bill Clinton)........teehee!

*SPECIAL NOTE* Does doing "it" on the hood of vehicles count? Cause if it does.....I have to revise this list! And Lil? You did say "etc."............so does a Boeing 747 count as well?