Way too many to list. Mine have been collected over many, many years. basically when doing a particular job, if you find you need a tool, buy it. Over time it builds up into a collection of tools which are actually used. Not in favour of buying stuff "in case I might need it someday".
For me: Jeweler's screwdrivers, both regular and Phillips X-acto knife with sharp blades Fine files, even an emory board Needle-nose pliers A good pair of rail nippers An assembly of paint brushes Plus the usual carpenter's tools (cordless drills, jigsaws, circular saws, hammers, clamps, etc) I'm pretty sure I missed something here, but this is what came to mind.
Amongst many measuring devices, a couple of steel scale rulers, a miniature tape measure, a very small square and a dial caliper.
A razor saw, small screwdriver set, diemakers' files,small vise, pin vise and various number series drills (bought as I needed them). Also, I use vernier calipers (if you're not familiar with them, get a pair of dial type instead) and a pair of 0-1" mikes among other items. CAD software is nice to have (a decent 2d package is is free at draftsight.com), and being a just a little crazy, I find a milling machine (no, I didn't buy it just formodel railroad use) useful for slicing and dicing plastic kit walls.
I make and or modify tools all the time to perform special functions. The one I probably use the most is an end nipper that I ground down the face to cut absolutely flush. It is razor sharp so I only use it on plastics and wood. But for sheet styrene it really comes in handy for shaping parts for complex building sides and roofs in my many scratch building and kit bashing projects. It makes short work of removing skirts from the sides of passenger car shells too.
What I use most, in no particular order: Dremel (var-speed), Small needle nose pliers, small set of screw drivers. I use most of what has been listed already. Does the small fridge I put under the layout count? I use it the most....LOL
My unknown brand snap-off hobby knife. My laptop (for getting information), especially this site. Good size scissors, for cutting track connectors (as they're stamped out in fours, so they have to be cut to singles). A flat blade screw driver, mostly for prying and tightening and loosening the screws on electrical connectors. My favorites are the old US-Made promotional ones with either a Philips screwdriver or a magnet on the other end. Also a good precision screwdriver set, for dissasembling (and of course, putting them back together) Dremel. Need a "new" one, as the 20 year old one Grandad gave me's battery has worn out. I'm considering getting one of the old Bakelite ones, or one of the new ones that is either electric or runs on AA batteries.
