Coolest Weapon.
 

I'm very bad at explaining, but I like the gun Vash hides in his arm (don't remember if it was the left arm or right arm :P).
When I first saw it I thought "Wooow!" , and in fact it's a really cool idea.
Regarding Wolfwood's cross, I was scared of it, don't know why, but a cross which in reality is a weapon makes me feel uncomfortable :heh:

that gun is awsome, I like it

not from Tri-Gun, but...
 

I know this isn't entirely on-topic, but the absolute BEST hand-gun in the anime universe is the main agent's gun from Wicked Beast City. Huge pistol that sends the user FLYING backwards into fences, walls and whatever else is behind him. Like a hand-held Wave Motion Gun.