Pristine Colt Python, 6" barrel nickel finish. Never fired. The previous owner took it home brand new and froze it in carbonite, only to be gifted to be somehow years later down the road.
Korth German DA .357 magnum revolver. I know enough about these $4000+ guns to want one. I'd take a 4" Korth with there silver plating finish (whatever it's called).
Any modern fully automatic firearm. New ones aren't legal for the general public and I have no desire to pay the prices for the old ones that can be had currently when I could get an amazing semi-auto for the same price. I'd be afraid of the resulting ammo price as well.
Unobtainable : Glock 18, Beretta 93r, any manner of full auto SMG.
Attainable : 6" Colt Python Stainless, Colt Delta Elite, Sig X5, H&K Mark 23, Luger, Mauser Broomhandle, That left handed 1911, FN FiveSeven, and an H&K P7M13
Something with a happy switch, but alas the prices for pre-ban full autos will forever keep me out the game. Even if I can one day afford it, I would never buy it as that same amount of money could be used for more "practical" purposes, and I am a very practical guy.