I have a soft spots for revolvers. They tend to generally be among my favourite weapons to track down and find, and depending on the game and genre, they also become the ultimate weapon to have around. Someone already posted the Broken Butterfly from RE4, so I'll also contribute with the S&W from RE5:
And who can forget the M6G Magnum from Halo:
On a side note, Prompto in FFXV gets a particular handgun (or handcannon, if you prefer it) called Lionheart, and I found it great too. I can't find any decent picture of it that doesn't feature Prompto, so here's this:
And going with the Lionheart motif, gunblades from FFVIII:
On an extra, final note, I have to mention this one particular weapon (can't find a decent pic of it): the modified Beretta, named M9, from Metal Gear Solid:
Because imagine how fun this thing would be. It basically incapacitates people, so it's a perfect non-lethal gun alternative, and despite having to be reloaded manually after every single shot, it can save you a lot of trouble and time depending on your life circumstances.