Thin rubber strands are nice, surprisingly thuddy with an after-bite somewhat like horsehair. These go for $115, I've made larger ones which cost more. I've got even thinner rubber I can use for these, too, although it tends to tangle.

I've made a few floggers with copper wire for the falls; visually striking, and pretty intimidating. These are very labor-intensive, and are priced individually. Used judiciously, they're pretty fun:
 

This rabbit-fur flogger I made is WONDERFUL, but the material is such a pain to work with, I'm not really doing them for other people right now.