If you don't mind staying in a big hotel, the
Eurostars Madrid Tower has opened this year and is worth checking out.
The
Silken Puerta America is also a great big hotel, with some very individual design bits and pieces (though a bit out of the centre).
One notch down from these two, I've had a great stay at the
Hotel Rafael Atocha, which is simultaneously central and quiet, and can sometimes be had for very little money.