Nobody listed the Muddler Minnow? Repent! And commit immediately to self-flagellation with a five-weight.
Anyway, here's my list:
1) Black Ant - Vince Marinaro wrote that he would choose an ant pattern over any other fly, including his own creation - the jassid.
2) Elk Hair Caddis - Great floatability, great visibility, great fly.
3) Black Woolly Bugger - a true classic if there ever was one, can be a baitfish, leech, etc.
4) Muddler Minnow - perhaps the best streamer on the planet. Gold tinsel body makes it a very good off-color water fly.
5) Adams - another classic, can represent several different insects.
6) Griffith's Gnat - maybe the best midge pattern around, mandatory on some spring creeks.
7) Hare's Ear Nymph - the definitive nymph pattern.
8) Stimulator - Can be a stonefly, a hopper, or a big caddis.
9) Royal Wulff - excellent attractor, made for rough water.
10) Blue-Winged Olive - A lot of olives hatch in a lot of places.
Honorable Mentions:
1) Clouser Minnow - another classic streamer, can be used on freshwater or the salt.
2) McGinty Popper (popper with yellow and black stripes to imitate a bee) - Bluegills and smallies love them. fun top-water fishing.