Of all the small additions I've made to my studio this year (like most smiths, I'm a bit of a tool fanatic!) my most used and loved has to be my Loritone tumbler. It really saves my hands from the repetitive work of polishing and lets me work on other pieces while the tumbler shines up my jewelry. It is also great for work hardening small items like earring wires.
I got mine from one of my favourite supply shops here in Ontario, workingsilver.com. The owner sometimes offers 10% discounts or free shipping. They carry the shot for the tumbler as well, and I highly recommend spending the extra money on the stainless steel shot to prevent rust!
It is not too tricky to maintain if you rinse your shot and barrel well after each use. I'll typically tumble between 30 minutes to and hour for most items.
Let me know what your favourite jewelry making tools/supplies are!