Historically, I've heard that guns used to commonly be combined with other weapons so they could still be used for defense if the gun misfired. (This pic isn't mine, but I saw one in a museum recently. It had a calander stamped on the blade, of all things.)
I've seen museum guns combined with rapiers, cutlasses, hunting knives, crossbows, axes... I've heard of gun-maces, but haven't seen any yet. They would bash heads very well.
I think the whole concept of a gun as a hand weapon may have had sound reasons at first, but I think it became more of a fad as time went on and guns became more reliable. We hardly even see bayonettes any more.
In popular culture, one of the better pistolwhip scenes I've seen was in "Equilibrium". With the push of a button a bunch of nailhead-sized things came out of the grip to make it more deadly, I guess. Lots o' gun choreography in that movie.
One of the most interesting gun/hand weapons I saw was in a museum on the East coast somewhere. It might have been just 100-150 years old: picture brass knuckles that could be unfolded to make a revolver. Unfold the blade from under the barrel, and it became a kris knive. I wish I'd taken a picture.
I think pistolwhipping is mostly a Hollywood thing, like silenced revolvers. If anything a bird's head SA revolver might lend itself best to the purpose, and a plastic auto would be the worst.