If I had to choose a favorite tool, it would have to be my torch, of
course, and second, my flex shaft, but in the last year or so I've
had some good luck buying used tools on eBay. I found a Kagan ring
stretcher, and I just love it. It quickly and easily rounds out ring
shanks (without significant enlargement, if you use a light touch),
as well as, of course, stretching them. Admittedly, my students get
more use from this last than I do.
I also bought a lapidary set-up and trim saw pretty cheap, and I
really enjoy cutting stones. The real joy comes, though, when I need
to adapt a stone to fit in a bezel, repair a chip, polish a
stone-back that I want to have show, or otherwise save a situation
with a cabochon. If I never scewed up, I wouldn't love these tools
so much, maybe, but now you know the dark truth.
Beyond that, I get a ton of use out of my belt sander. It is a
cheap, hand-held Black & Decker model ($30 or $40) that cleverly
comes with a pair of clamps to hold it belt-up to a workbench. (It
is gratifying to see even a low-end object like this encorporate
good design features such as this!) Very handy for quickly
generating a straight edge on silver sheet.
I was trying to think of something I use that isn't on every
metalsmith's bench, but it's all pretty standard. The only "novelty"
has been covered here a few times, so if you're new, look in the
archives for "titanium V's". I still use them nearly every day.