A decent flash for $100?
Let me recommend the flash I've been using for the past year: the Metz 36C-2
MZ53622 Metz 36 Series C-2 Auto Aperture Manual Shoe Mount Flash, Non-Dedicated, Guide Number 118, ISO 100 ft.
It's small and light, and it has enough power for most situations.
It's not dedicated, but it is results are consistent.
It has 3 auto f stops, and only one manual setting - full power, but it performs very well for its price.
I recently bought a Pentax 540, but haven't used it enough to comment on it, but the results it's given me so far are excellent.
One of the main things I bought it for was fill for outdoor portraits when I have to shoot quickly, and it's done well.
Getting back to the Metz, in my opinion you can't go wrong with it for the price.
I would also suggest the Sunpak 383 super as Heather did in post #20.
I owned two of them for about ten years, and they never let me down.
I gave one away, and left the other at a model workshop, never to be seen again.
Metz 36C-2 or Sunpak 383.
Good luck.
Mike