Long fluorescent fibers for streamers or baitfish. You can also use Fluoro fibers to add lateral lines, tailing material or just spice up your streamers. Very fine, high movement qualities when in the water.
It's also great for tails and legs on nymphs, such as the popular Ju-Ju patterns from Charlie Craven
Flash 'N Slinky is a great baitfish body or tailing material comprised of Slinky fibers and Gliss-N-Glow. It has tremendous shape-holding qualities with the right amount of flash to it. Plus it comes in 10 inch lengths to tie up even the biggest of salt-water or streamer patterns.
Angel Hair is a very fine Mylar type material that is sold in Hanks. With 6-8"strands, Angel Hair can be used for those big old billfish flies, cut it up for dubbing your small trout flies, or just to add a little glitter to your old standbys. Tied in baitfish patterns like deceivers and clousers, Angel Hair seems to come alive in the water.