Car shakes at different speeds

I have a new 2007 toyota camry(2,341 miles). We got the car w/ over 400 miles already on the car. (They drove the car to dealer). I noticed a little shake in the car (passenger seat would shake). I thought maybe tires just needed to be balanced. But we were getting new rims and tires so didn't take it back to dealer, thinking that would fix the problem. After the new rims and tires it was shaking noticably. Took the car back a week later. They made it worse. Took it to a local tire place and they said a couple of the tires bounced a little on the machine. Took it back to the rim and tire place and they said no it was balanced wrong. Needless to say it still was shaking. Took it back and they went ahead and put a different brand of tire on the car and it still shakes at different speeds. What do I do now? Should I take it to the toyota dealer? I'm thinking maybe it is something else and not the tires.