Quicksilver (or possibly the Flash?)
He would always have the Speed passive power, as well as the Haste passive power. Maybe you would invisible when standing completely still (in the comics, they would always "vibrate" to such a point that no one could see them)?
Spider-Man (yeah, yeah, I know we've gone over this before).
I guess for this character, you would kinda switch between powers like weapons (like in the human torch player class). You could switch between web-swing (grapple hook in the form of a web), stick to walls, and web-ball (like freeze ray, only in the shape of a sticky ball... upon impact with player "wraps" them up in webbing. Could probably just do this with some kinda shader or skin). Also, passive power would be Spider-Sense (screen would pulse red when missiles are incoming, or maybe when an enemy has their sights set on you for more than 3 seconds).
Player would be shaded like ice. Could switch between powers like freeze ray (basic player freeze power), freeze blast (ices floor, makes it slippery. also, when used on water, freezes all players within instantly), and ice ride (player points crosshair at ground, holds down fire button, player "slides" very quickly in the direction he is facing).
I have just been thinking of these, and if any are impossible to code, it's no big deal. I really don't know much about what the Engine of Quake 3 can and cannot do, so these are just suggestions.
What do you think?