<Ahnold>Phased plasma rifle in the 40-watt range?</Ahnold>
The Noisy Cricket would be particularly easy to EDC, takes up practically no room...
A Dalek energy weapon would be nice as well, especially one of those Tommy-Gun style Dalek guns from the NewWho episode "Evolution of the Daleks"
Danny Vermin's 88 Magnum "It shoots through schools" from Johnny Dangerously
as far as *real* TV/movie guns go, I've always liked Bronson's Wildey .475 from Death Wish 3, and Sledge Hammer's .44 Magnum long barrel revolver