The Zebra Midge has been around a long time because it consistently fools trout.
They are fast and cheap to tie. I tend to use #18 but they normally range in #16 to #22. These are money on the Little Truckee. Put this on a tag with a larger nymph below to get it down or use it as a dropper off of a dry. I never fish with out these simple and effective flys.
Check out the video from TightLine Productions on how to tie your own.