Flip Flops make a great source for fly tying foam. They come in alot of colors, and you can usually buy a pair for a buck. One pair of Flip Flops will make hundreds of bugs.

I cut the flip flops into strips using a power scroll saw. You can then cut the strips into appropriate sized chunks. Round off the corners a bit, and attach to a hook. Add a few rubber legs, and you're ready to fish.