CROWBAR: Just your standard crowbar, back from the first game. This time you should expect to be interacting a lot more with the objects you come across in the game. So smashing and bashing through some areas with this tool will make it quite handy at times.
GAUSS GUN: The gauss gun was in the original Halflife, and will make its comeback this time on a mounted vehicle that you can drive. Though who puts a gun on a vehicle and doesn't make it detachable.
GRENADE: Simple but effective. What action game doesn't have one of these brutal stones of thunder? In the E3 demo they show very realistic use for the grenade to send your enemies flying through the air. Its got a timer that goes off once you pull the pin, so don't stand there and daydream for too long.
GRENADE LAUNCHER: The best way to teach your foe how to fly. Just another of the exciting new weapons in Halflife 2.
M-29 OICW: That's Objective Individual Combat Weapon. This is basically a futuristic version of the M-16 that comes complete with a zoom, grenade launcher, auto range finder, auto wind adjuster, and enemy identifying indicator
THE MANIPULATOR: Of all the new weapons in the game this is the most thoughtful and creative of them all. If you've seen the game play movies available for this it shows how useful it can be when your low on ammo. It gives you the ability to lift objects into the air, such as bodies, furniture, trash cans, tables, or whatever you so desire. Alt fire can propel the objects through the air at your target to dish out half decent damage.
MP5K: This appears to be a mini version of the MP5 featured in the original Halflife. Though it is small, its no bee bee gun.
MP-7 PDW: Personal Defense Weapon. This weapon appears to be small for the amount of ammo and accuracy it can dish out, but its also a futuristic type weapon, which means improved technology.
PHEROMONE GRENADE: A brand new type of alien weaponry. This pheromone lets you trick and deceive ant lions to do your bidding. Basically, where ever you throw this, the ant lions will follow and consume everything in its path (except you of course) until it is killed.
USP MATCH: This is just a standard pistol. Its also used currently as the default pistol for the CT team in Counter Strike.
ROCKET LAUNCHER: As seen in the previews, it did a fancy job of quickly taking down enemy aircraft. It has a laser guide system which allows you to just shoot it, and then paint it when a red dot to guide the missile the rest of the way home.
SPAS-12: This is the shotgun returning from the original Halflife. Apparently you can also be damaged from the shells backfire. Otherwise its great for close quarters combat, and packs a real nice punch.