Stimulator if there are caddis or stones or hoppers around. Elk hair caddis if there are caddis around and the dropper is light. Foam ant or beetle if you're in the woods and nothing is hatching. Daves Hopper, Henrys Fork Hopper, or Foam hopper if you're in a grassy area and nothing is hatching. Yellow humpy if there have been light-colored mayflies hatching recently. Badger bivisible if you're feeling old-fashioned. Other impressionistic hopper/stone/caddis imitators (Turck's Tarantula, Madam X, Sofa Pillow, etc.) work too. Also some of Gary Lafontaine's closed-cell foam patterns (Air Head, Cone, etc.) might be fun to try, although I've never done it.