Please PM additions or corrections to tyme at either TheFiringLine.com or TheHighRoad.org.
There is a newly-created wiki at IMFdb.org that aims to catalog firearms used in movies (and maybe TV too, I'm not sure). Since the wiki structure is much more suited to this task, I urge everyone to contribute there. Perhaps also pick an entry or two from this list and add it to that wiki.
Zoe: Mare's Leg (modified Winchester model 92 .44-40 lever action)
henchmen: Beretta PM 12S
La Femme Nikita (TV)
Mostly glocks, berettas, and a few mp5s
Law and Order (TV)
Lenny Briscoe: S&W Chief's Special
Joe Fontana: S&W Model 19 (.357mag)
Law and Order: Criminal Intent (TV)
Craigan: Benchmade Mel Pardue
Lost (TV)
1x03 - The marshall's gun (first gun seen on the island): SigPro (referenced as a 9mm, so either a 2009 or 9mm 2022)
2x04 - John Locke checks out an HK PSG-1
2x11 - the guns they leave behind are a glock, an AK, a 1911, and two guns that look like Sigs
2x?? - Zeke (when the Losties get ambushed the first time): Luger
2x?? - Desmond (in the hatch): MAK 90
Locke has some stainless spyderco clipped to his vest most of the time
various: Kate's backpack is a Black Diamond Bbee
Miami Vice (TV)
1x01 - Crockett uses a Browning BDA (Sig P220). After that, Jim Zubiena (the assassin in episode 4 / hour 5) suggested to Mann that Crockett use the Bren Ten.
1x05 - Assassin (played by Jim Zubiena) uses 1911s, some rifle, donuts with sprinkles, and coffee
1x08 - arms dealers: M60 and an uzi?
seasons 1 and 2 - Crockett: Bren Ten
seasons 3 and 4 - Crockett: S&W 645 .45
season 5 - Crockett: S&W 4506 .45
misc - Crockett: Detonics Combat Master as a BUG.
NCIS (TV)
Gibbs: Gerber, Kershaw Leek
Ziva: Cold Steel
Dinozzo: Spyderco Endura
McGhee: Spyderco Native III
The Unit (TV)
Microtech Halo 2
Benchmade 550 Griptillian
Veronica Mars (TV)
Veronica's camera (pilot) - D100 (verified... it is NOT a D2H)
Veronica's camera (1x..) - Nikon Coolpix 5700 or 8700 (NOT an 8800)
Veronica's camera (2x..) - Nikon D70 (in 2x03, w/ a 80-400mm VR lens, see 12:45)
Veronica's phone (1x..) - Samsung E715 (see 1x04 18:40)
Veronica's phone (2x..) - T-Mobile Sidekick II
1x07 - Walther PPK (the artist)
1x07 - Keith Mars - Beretta 92
1x18 - the undercover ATF agent has an HK SL8
2x03 - Logan at the range - Glock
2x22 - Cassidy - Beretta 92
Witchblade (TV)
1x?? - Steyr AUG (the super sniper gun used in one episode)
The Vector/Vektor CP-1 was recalled in 2000 due to a defective (or non-existent) drop safety. That means the gun may fire even if the trigger isn't pulled.