I did have a ABS light on a few months ago. It was a bad bearing that was causing that. Jacked the car up and wiggled the wheel. There was lots of play in that bearing. The strange thing about that bearing is that it was not making any noise. I have replaced 3 other bearings and they all were making lots of grinding noises. So now I am up to 4 bearings replaced, 3 on the driver side and one on the passenger side. After replacing the bearing I noticed no improvement in the vibration/shaking problem. Like I posted earlier I will be replacing the passenger drive axle this weekend. Hope it makes a difference.

I've had vibration problems for a while. By the time I really started to check, I found three bad tires (wheels OK).
I still had some vibration and seemed to be getting worse. I had some pulsing pedal and steering shake on braking. I replaced all four rotors and cleaned the wheel hub faces really good. All vibration gone.
So, I think you have a rotor problem.

I had this vibration on my 01 SSEI. At like 68 mph it was like someone flipped a vibration switch on and the car vibrated badly
I know this is WAY out of left field but I replaced my rear air shocks and my vibration went away.
??????
I knew they were bad for a while. I would jack up the car and see the fluid leaking out, till it all leaked out. Recently it also sounded like a flat tire (air psi leaking out). in the left rear.
I installed last night and on my exrpressway drive to work this morning there was no vibration.
I am not recommending that anyone throw rear shocks at their car for this but I guess this is what fixed my car.

you know its interesting that you guys mentioned rotors. before i even read this rotorr reply i put pads and rotors on this afternoon due to a bad highway brake pulsation. I cleaned the hub surface really good and lubricated everything. i found i had a bound up caliper slide pin as well which i freed up. its much better now but still has it a little. i think the rest may be in the tires or possible out of balance. i guess ill try to balance them for the umteenth time and see if that helps. the tires arent gonna make it till next winter anyway.