1- Elevator
An elevator is always a great place to engage in very quick sex, although going up or down several floors isn't usually sufficient time to get off. I recommend you stall the elevator (given that you don't trigger any alarms by doing so, unless you enjoy getting caught), penetrate, and when you're done and let the elevator run again, don't exit from the main floor.
Ideal position: Upright wheelbarrow (with her facing the wall, hold her up by her thighs, placing them on either side of your hips, while she holds on to the wall).
2- Movie theater
As cliché as it sounds, getting busy in a movie theater is always a thrilling experience, and there's less chance of getting caught (unless of course, she's a screamer, but if it's horror flick, you'll be okay). Movie theaters are best for oral sex, so get your girl to go down on you in your local movie house today.
Ideal position: (Besides on her knees) Her sitting on top of you, facing the screen.
3- Back of club/restaurant
Being out on a hot date talking about hot things with a hot girl will usually excite you, so if both of you are up for it, head to the darkest part of a nightclub, or even the bathroom, and get your bang on. Chances are people will hear or even see you, but if you have an little exhibitionist lurking within, it's all good.
Ideal position: Standing, upright doggy.
4- Stairwell
If your roommate's home, or you and your girlfriend only have 10 minutes to spare for a lunch date, head to the stairwell of a building with an elevator, preferably on a really high floor, and go crazy for a few minutes.
Ideal position: Missionary, with her back arched over a stair.
5- Car
So it's not an original idea, but a quickie in the car, at a location where you won't be arrested for public indecency, can be a very memorable experience. If you're short on time but big on horniness, then do it while you're driving. Just kidding -- take a few minutes to enjoy the view inside the car.
Ideal position: Doggy in the backseat.
6- Alley
Before you begin envisioning rats and drunks, picture an alley behind a restaurant that isn't as filthy as those you see in movies. Ideally, she'd be wearing a skirt and the both of you could head to an alleyway just after dinner and before the show. Now that's what I call an intermission.
Ideal position: Standing up, with one leg wrapped around you.
7- Office
Whether it's a babe you've been eyeing at work or your girl shows up in nothing but a trench coat and heels, sometimes sex at the office is part of what makes life that much better. Make it part of your daily tasks, if possible.
Ideal position: Her back against the wall, and her legs wrapped around your waist. Or, she can always spread 'em on your boss' desk.
8- Dressing room
How many times has your girl got you all hot and bothered while she's changing in the dressing room of a clothing store? Well, why not add some kick to the tedious task of shopping by sneaking into the changing room with her and giving her a little taste of your dressing?
Ideal position: Standing doggy.