Could be a worn CV joint in the drive axle.Had it happen in my last car.Alignment and balance wouldn't fix it.The vibration, though not violent, at 70 -75 mph was enough to numb my hand on longer trips.Something to consider if your rig has alot of miles on original axles.Say around 100,000 or more.

the car has 68xxx miles on it. Maybe it is the CV Joint though since its not a violent shaking, just a vibration in the steering wheel.

I have to believe that it is not something to do with just one tire since i had them all rotated, which would take the bad wheel from the front to the back, and it still vibrates through the steering wheel. Also, the shop i go to checks for malfunctioning parts and bent rims, and I had neither.

Is there anything in the suspension that would cause this?

I guess the CV joint is a possibility. Have the boots ever been ripped/replaced. Ya know, nobody has mentioned the brake rotors. It'* possible they could be the source of your problem. Some shops can balance your tires with the wheels on the car. Just a suggestion.