Silvey's Yellow Sally is a winner. I don't go anywhere in the Summer without a few of these in my box.
Essentially a small, yellow-colored stimulator, the Silvey's Yellow Sally works great not only during Yellow Sally hatches but practically anytime the fish are looking up. This fly floats great, is easy to see, and great with a dropper beneath it. This fly is deadly during the tail end of golden stonefly hatches when the fish are warier because it is small but still has a golden stone look to it.