My all time favourite mod is LED's. Really makes inserts pop, they serve a purpose in less heat and I have not had to replace many, not like globes that seems to be a full time job in replacements. Moving tiger saw I think is my fav.
Least and I got it for nix basically on eBay is the upright coin for a tz. The boss of rtbb hates it so much there's more expletives in his sentences than actual words when he describes it.