The Butterfly Bistro is one of a number of restaurants in Karon, just off the beach road in "The Old Phuket" avenue, easy to find and always busy. We only went there for lunch a couple of times, they have a Thai menu but they seem to focus more on western food. We liked to take a break from Thai food for some western favourites for lunch occasionally.
Butterfly bistro has good food that comes out quite quickly. Fairly busy for lunch also, which is good.
Cheap prices (600B for 2 people, a couple of beers/soft drinks each + a western snack/meal like club sandwhich or burger with chips). And as seems to be the custom in "The Old Phuket" avenue, free chilled refresher towels when you are seated.