The whisky sour (with bourbon) has three dashes of Angostura bitters in its recipe. However, David Embury suggests that Peychaud combines better than Angostura with scotch (in his recipe of the Bobby Burns). So, I tried adding three dashes of Peychaud in a Scotch Sour. You should try it too, in my opinion... ;-)
This cocktail is also great without any bitters.