In Season 2's "Euphoria, Part 1" (S2E20), Baby Shoes (Chioke Dmachi) uses a Ruger SP101 to shoot officer Joe Luria (Scott Michael Campbell) during the opening chase. Dr. Gregory House (Hugh Laurie) tests a theory by using a similar Ruger SP101 revolver with a spurred hammer to shoot an already deceased cancer victim in the head and putting the body in an MRI machine with destructive consequences. The SP101 makes another appearance when author Alice Tanner (Amy Irving) uses one in a suicide attempt in Season 7's "Unwritten" (S7E03).
Glock 17
In Season 2's "Euphoria, Part 1", Officer Joe Luria (Scott Michael Campbell) is seen drawing his Glock 17 on a suspect at the opening of the episode. In Season 5's "Last Resort", Jason (Željko Ivanek) uses this third-generation Glock to hold Dr. House (Hugh Laurie), "Thirteen" (Olivia Wilde) and several patients hostage.
Glock 21
The Glock 21 is seen used by Jack Moriarty (Elias Koteas) in Season 2's "No Reason".
Heckler & Koch USP
In Season 6's "The Down Low" (S6E10), a thug named Tommy (Preston James Hillier) pulls an H&K USP on Mickey (Ethan Embry), who is soon to become House's patient. Mickey wrestles the USP and gets Tommy to shoot himself in the foot, and the loud sound makes Mickey pass out.
Heckler & Koch USP Compact
In Season 5's "Simple Explanation", what appears to be a Heckler & Koch USP Compact is seen on the floor of a bedroom.
Colt M1911A1
L.K. (Brett Wagner) uses an M1911A1 in a diner robbery in Season 3's "Fools For Love" (S3E05). In Season 8's "Perils of Paranoia", Wilson finds House's M1911A1, which House succeeds in convincing Wilson is a prop, despite the fact that the cartridge House chambers is clearly not a blank.
Colt M1911A1 (Stainless)
In Season 7's "Two Stories" (S7E13), House (Hugh Laurie) uses what appears to be a nickel M1911A1 in a parody of a scene from Pulp Fiction.
SIG-Sauer P228
Police officer Donny Compson (Jon Seda) and his partner (Jeff Corbin) carry SIG-Sauer P228s when chasing a suspect in Season 6's "Brave Heart" (S6E05).
SIG-Sauer P226 (Nickel)
Dominika House (Karolina Wydra) uses a nickel-plated SIG-Sauer P226 while at a pistol range with Gregory House in Season 8's "Body and Soul" (S08E18).
Beretta 92FS Inox
Darrien (Amy Landecker) hallucinates that someone is pointing a Beretta 92FS Inox at her.
Colt Python
Diner robber Bobby (Scott Rinker) in Season 3's "Fools For Love" (S3E05) uses a blued Colt Python.
A stripper pulls a Smith & Wesson Model 60 on Dr. Chris Taub (Peter Jacobsen) in Season 7's "After Hours" (S7E22).
Rifles
M4A1 Carbine
The M4A1 carbine is seen in the hands of Marine Sgt. John Kelley (Marc Blucas) in Season 3's "Top Secret" and carried by SWAT officers in Season 5's "Last Resort".
M16A2 Rifle
In Season 3's "Top Secret", House is seen holding an M16A2 rifle, fitted with an ACOG scope on the carry handle and a RIS handguard in place of the standard A2 handguards in a dream sequence.
In Season 6's "Wilson" (S6E09), Wilson (Robert Sean Leonard) and Tucker (Joshua Malina) are seen turkey hunting with Remington 870 Express shotguns. Wilson using a 12-gauge with a red dot sight and turkey camo, and Tucker with a 20-gauge and wooden furniture.
Mossberg 500 Cruiser (combined with walking cane)
In Season 7's "Bombshells" (S7E15), House is seen turning his cane into what appears to be a Mossberg 500 Cruiser shotgun fitted with a pistol grip and weaponlight in a dream sequence.
Other
Ramo RT-37
One of the prison guards in Season 8's "20 Vicodin" can be seen with a Ramo RT-37 during a riot.