USSS Agent Frank Horrigan (Clint Eastwood) uses a Smith & Wesson Model 19 at the start of the film to arrest Mendoza (Tobin Bell) and kill his two henchmen. Later on, a Secret Service agent holds a Model 19 on Horrigan before he disarms him.
SIG-Sauer P228
USSS Agents Frank Horrigan (Clint Eastwood) and Al D'Andrea (Dylan McDermott) carry SIG-Sauer P228 pistols as their sidearms in the film, as do all the other Secret Service Agents.
At the start of the film, Mendoza (Tobin Bell) hands Frank Horrigan (Clint Eastwood) a nickel plated Llama III-A to kill Al D'Andrea (Dylan McDermott) after he discovers he is a Secret Service agent. Frank weighs the gun as he approaches and convinces Mendoza he isn't Secret Service by clicking the gun to D'Andrea's head, aware it was in fact empty.
Composite Pistol
Mitch Leary (John Malkovich) builds a plastic Composite Pistol with two barrels as an assassination weapon to kill the President of the United States. While it is questionable how well the composite material would withstand the high pressure gases from firing, it is used several times in the film without ever breaking. When at the hotel where the President is staying, Leary assembles the weapon under the party table (after practicing assembling it blind folded several times) and had previously hidden the ammunition in a rabbit's foot keychain, and the springs in a pen. The weapon appears to use .32 S&W Long ammunition.
IMI Uzi
When the Washington DC Metropolitan Police attempt to arrest Mitch Leary (John Malkovich), the DC ERT officers are armed with IMI Uzi submachine guns with stocks extended. Unfortunately, it turns out that Leary scrambled the trace and lead the Secret Service and the police to a completely different address. Uzis are also seen used by the Secret Service agents when they rush the President out of the hotel after the assassination attempt.
Colt-Sako Rifles are used by the two hunters that walk up to Mitch Leary (John Malkovich) after they hear him fire his Composite Pistol.
Winchester Model 70
Winchester Model 70 rifles are used by Secret Service Counter-Snipers at the hotel.
Steyr SSG 69
One of the Secret Service Counter-Snipers uses a Steyr SSG 69 rifle with a five round magazine and double set triggers.
Beretta 92FS
LAPD officers are seen with Beretta 92FS pistols while escorting the President out of the hotel after the assassination attempt.
Unknown Pistols
There are several pistols seen in the film that are either too blurry or too hard to indentify.
Looking at the Magazine Butt, I'd say a Beretta 92. - Thomas.
Gun Rack
When Horrigan (Clint Eastwood) is taking a nap on the job, a rack full of guns is seen behind him, although it is too far from the camera to properly identify them.