If you collect insulators, these are highly recommended products.
1) Oxalic Acid (Wood Bleach) - Great for cleaning most filthy glass insulators. Just soak them in a bucket of this for a few days (or weeks for the really filthy ones) and they'll come out looking brand new. Warning: Do NOT use with carnival, flashed amber, or opalescent glass! Be sure to read this page on proper insulator cleaning!
2) Museum Gel - This stuff is awesome for keeping your insulators on glass shelves and helping to prevent them from moving around or falling off. Sticks well but is easy to remove. Use them between two-piece transposition insulators instead of wooden dowels!
3) Collapsible Hand Truck - These are lifesavers for toting all those boxes of insulators around, especially going back and forth to an insulator show. Whether you buy or sell, you definitely appreciate having one of these.
4) Digital Caliper - If you're interested in documenting insulator sizes, variants and embossings to a highly accurate degree, these eliminate the guesswork that you'd get with a ruler or a measuring tape.