Favorite stock exhaust EVER... Mustang GT
Also pretty beastly:
And one more...
My personal favourite exhaust sound EVER... Porsche Carrera GT with straight pipes. I am fortunate enough to ride in one of these. Even stock it sounds amazing. Straight pipes make it absolutely amazing. Its pretty funny to see the look on everyones faces riding in it. The sound, the look of the car... everything just makes for some pretty funny expressions on peoples faces.