Both the straight and the little 90' die grinders are handy, i even have a cheap harbor freight electric straight one i use on the welding rig, handy for cleaning up torched holes sometimes. The carbide bits are not cheap, and you gotta make sure they don't pull out because it's like a bullet bouncing around. They make rotary tiger paws (flap disk), nothing better for shining up for a tig root, and the spin on sanding and scotchbrite pads turn the right angle type into a very controllable setup for fine work. When welding tractor cabs we used anti spatter spray to coat the fenders and floor, a 4" masonry chisel for chipping berries after welding, and then polished up auto body style with the right angle grinders, topping the welds so they could be safely blended with a caulk and making everything completely smooth, first with 80 grit, then wet used up 80, then the scotchbrite.
They also make extra long carbide bits, sometimes doing repairs nothing else works. There's the little cutoff wheels, nice to buy a cheap dedicated one with the gaurd, good for blind cuts. The little wire wheels are amazing for cleaning slag and stuff, and they make both wheel and cup types. They have a scotchbrite flap disk that polishes stainless tig welds beautifully, i gotta remember to ask for one of those. Another really good option for grinding the inside of stuff is a cone wheel on a grinder, they make various sizes and shapes for different things.
Huge fan of bending rods, super handy. I use a 1 position stinger, and I'll bend almost every rod i run, a 90 right where it comes out. This allows me infinite rod angle adjustment for the most comfy position, and it can be adjusted as you go by simply pushing on it. It also allows you to put the lever in the back so it's out of the way, and makes for a handy hook to hang it on your pocket when tacking stuff up. In tight spots, i most often find bending (or using the dedicated groove on a tweco) the rod straight out in line with the handle, minimizing the room it needs to fit somewhere. There you can do another bend or two as needed, and it moves your hands a bit further away so you can cram your head in there deeper. It surprisingly can really make the difference sometimes, so much so that's my sop if i gotta bend one. You can also vary heat by adding bends, it creates resistance cooling the puddle on the fly, handy when your machine is a ways away and you need to turn down a touch in a spot.
