The Clouser Minnow is probably the most all-around useful fly ever created. It will catch nearly any freshwater or saltwater fish. The Clouser imitates nearly any baitfish depending on the color scheme, and can even imitate crayfish, shrimp, or crabs. The fly naturally rides hook point up, helping to avoid snags. This fly is most commonly tied with darker colors on the fly's back (while it's swimming) and lighter colors on the belly.
The Woolly Bugger is one of the most effective fly patterns ever invented. It can catch nearly anything that swims and can be tied in hundreds of variants of color, weight, and materials.