There are many current and many defunct air gun manufacturers. This is a semi-complete list of these manufacturers. Feel free to add more manufacturers to the comment section below. Eventually this will be made into a form that allows folks to add their own air gun along with information such as velocity, weight of pellets etc to document FPE.

Aftermath
Air Arms
AirForce
Airgun Brand
Airrow
Anics
Anschutz
Armscor
ASG
Avanti
Baikal
BAM
Beeman
Benjamin
Beretta
Blackwater
Browning
BSA
Colt
Cometa
Commando
Crosman
CZ
Daisy
Dan Wesson
Daystate
Diana
Droid
Eun Jin
Evanix
Feinwerkbau-FWB
FX
Gamo
GAT
GEM
Hämmerli
Hatsan
Heckler & Koch
IHP
Industry Brand
IZH-Baikal
Kunitomo
KWC
Legends
Logun
Magnum Research
Marksman
Marlin
McGlashan
Mendoza
National
Parker Hale
Relum
Rohm
Ruger
RWS
Sam Yang
Sheridan
Shooting Star Inc
SIG Sauer
Slavia
Smith & Wesson
Sportsmarketing SMK
Sterling Armaments Company
Steyr
Stoeger Arms
Swiss Arms
Tanfoglio
Targeteer
Tech Force
Theoben
Umarex
Walther
Webley & Scott
Weihrauch
Winchester
WinGun