The Shake-Weight was already sexual, but check out the homo-erotic Shake-Weight for men commercial. I love their reaction when they finish.
Perhaps the original sexy workout device, the thigh master had a bunch of my guy friends dreaming about Suzanne Summers when they were home alone.
The Hawaii chair forces you to thrust your pelvis. It's sort of the same action as a hula-hoop, but without the hoop... and sitting down... which looks pretty sexual. They also claim you can do just about anything on the Hawaii chair. Watch guy in the fuchsia shirt. He's sooo into it!
The Rock-n-Go infomercial seems to have disappeared. So here's a clip from a review of it. Like the Hawaii chair, this one looks like it gets your crotch moving (although it actually claims to be a core workout) The difference is that the Rock-n-Go gives the sexual cowboy effect - that is, thrusting your hips while on horseback.
This last montage is for the Gazelle. While the workout machine itself isn't exactly sexual, Tony Little is.