Sheesh, it could be any number of things. Like said before, bushes, bearing, engine mount etc
Probably not a separated tyre if you have changed them and had the new ones balanced hmmm... Have you tried rotating the tyres from front to back? If the vibration moves from the steering wheel to the rest of the car after rotating the tyres, you know it was the front tyres.
Assuming the tyres are new, if they are distorted from sitting for ages, they could balance fine but still cause vibrations.
Check the discs as well, could be warped.