I am partial to the V10 sound for obvious reasons. I think the LFA is massively overpriced but there is no denying that it sounds amazing. And of course the Carrera GT sound is a classic.
For ultimate sound on a street car though I would have to say the Zonda F is right up there.
For ultimate sound on a race car (besides F1) I would have to go with the Aston Martin LMP or the Zonda R.