In "Gatherings", Mike (Nick Frost) brings a Generation 2 Glock 17 to Daisy's (Jessica Hynes) party on Tim's (Simon Pegg) request. He keeps it with him as he "guards" the flat's door, but thankfully, never uses it. He does, however point it at Tim threateningly during their fight, only to have Tim casually slap it away.
Remington 870
In the opening of "Art", Tim (Simon Pegg) uses a sawed-off Remington 870 fitted with a pistol grip, and vertical fore-grip during his speed-induced Resident Evil 2 fantasy. He kills two zombies with it before he is distracted by Daisy, snapping him back to reality. When he returns to his fantasy, he is quickly "killed" by zombies that have taken the opportunity to advance on him.
Beretta 92FS
In "Chaos", Mike dual wields two Beretta 92FS when he and Brian (Mark Heap) hold a guard at bay while Tim, and the others rescue Colin the Dog from a testing laboratory. During Tim's infiltration, the two quickly befriend the guard, and Mike even allows him to hold one of the pistols. He gives the other to Brian, who (dramatically) remarks on how cold it feels in his hands.
Heckler & Koch MP5A3
Seen in the hands of Mike on various occasions.
MAC-10
In a direct parody to Pulp Fiction in the episode "Back", Daisy returns home to find a MAC-10 belonging to Mike sitting on her counter. When he exits the bathroom she jokingly holds the weapon on him before Tim arrives. Later, in the same episode, another MAC-10 is seen sitting on Daisy's bed, which Mike had been using in her absence.
In "Change", Mike is briefly seen holding a MAC-10 when he, and the rest of his flatmates are investigating the noise caused by Marsha arguing with her daughter.
Uzi
In "Back", an IMI Uzi with it's folding stock removed can be seen on Daisy's bed.