Originally posted by Accord1278
Yup, have all of your wheels balanced (high speed balancing) and have them rotated as well. When you get your wheels rotated, make sure they torque them down properly and in the proper order they are supposed to be torqued. Just make sure everything in your suspension is pretty tight as well, like no loose bolts, etc. There is a slight chance that you might have warped rotors. and also check to make sure that none of your rims are bent or damaged.
I'd check all of the items Accord1278 posted.
1. Bent wheels (check inside and outside of the rim for bends and cracks) can cause vibration while driving
2. Unbalanced tires (weights may have fallen off) can cause vibration
3. Improperly mounted wheels
4. Broken engine mounts
Does your car shake when you press the gas after going 40+ MPH or is it just dependent on vehicle speed?