I agree. The Super Shotgun (along with most of the other Doom weapons) was just really fun to fire. The fact that it tore most smaller, fleshy enemies to bits when it hit them just made it so much more fun.
Remember the Particle Cannon from Wolfenstein? That fits this perfectly. There's a distinctive, high pitched whine, followed by a beam of pure destruction spewing from the front of the gun, literally vaporizing any Nazi who gets in the way.
Someone mentioned the Portal Gun as well and I must agree. Just that sound...
Also, who says it has to even be guns? Who doesn't love the brutal, mighty uppercut move from Mortal Kombat?