Off the top of my head...
Don't remember the name of it but there was a hopper that fed from a giant ball. The ball separated from the neck (which threaded right on to the gun), so you could keep a bunch of the balls hanging from a special belt and swap them out instead of reloading. I think it was called the "Electron" something but wasn't electronic at all.
Then there were "Speedpods" from JT which, instead of a door, had retractable teeth held together by an o-ring. They came with a special "collar" which mounted to your Viewloader Revolution that replaced the door. It expanded the capacity significantly, and featured a game timer. Rather than open your loader, open your pod, then dump paint, you just crammed the pod into the collar which pushed back the teeth and released the paint (and pinched your hand real bad).
For a while there were clear barrels made by System X and 32* which had a metal back, and a clear plastic front in various colors... They made grips and volumizers and site rails too. The System X ones tended to crack and craze but the 32* ones weren't too fragile (no porting) but they weren't especially good.
Then there were KK "ring" triggers for the Angel and Shocker, short and tall. The short you put your index finger in the ring, the tall you put your middle finger in the ring and your index above it. I think they got banned because of some perceived speed advantage, that and a lot of people cut their trigger guards.
I recall having a sidecar for my Automag that held a squeegee along the barrel like a ramrod, so you could quickly pull it out and swab after you had a break. The bottom of the foregrip popped out and was a barrel plug. Then I had an Angel with two volumizers, except the nonfunctional one in front of the battery was actually a cleverly disguised tool kit.
Uhhhhhh I'm out for now, back when my brain recovers.