I would like believable/plausible weapons like in Shadow warrior. Not like ones that Lampsy feller showed.
Now i'm not sure if you're serious or not, because the first one he showed was a real handgun and the other is based on it. I really like the Mateba style weapons.
Anyway, Bixi did actually raise a pretty good point. (It was raised before, long ago, but we can't expect everyone to trawl a few hundred pages of forum posts can we...)
Ammo options. It is very difficult to get more stopping power, (per individual round - we are leaving RoF out of this for now,) from a weapon by modifying it. That baseline is supplied by the ammunition.
I would really like to see some 'experimental', (read that as "Highly volatile and potentially suicidal to use but GOD DAMN it hits like a train!") ammunitions out there. Highly illegal and seriously black market military grade stuff.