Here are some new weapons for a sci-fi setting. They're designed to be relatively mundane items in a futuristic game. In a modern game, they have a Gadget Rating (from Pulp Zombies). Unless noted otherwise, treat the gadget rating the same as a Superscience Power Level.
Equalizer Pistol
Enforcer Pistol
Plasma Rifle
ASMD Shock Rifle
Phase Stream Projector
Van de Graaff Pistol

The Equalizer is an advanced version of a modern pistol. It features an integrated laser sight and gyro-stabilization system, which grant a +2 bonus on any Aiming rolls. The factory model holds ten rounds, and is in all other respects identical to the standard Pistol from the BtVS RPG Corebook. There is also a common submachine gun built using the same technology called the Black Adder, which has a 30-round magazine and is otherwise identical to the Submachine Gun from the BtVS RPG Corebook. Any rifled cartridge firearm may be modified with Equalizer technology, although the stabilization system experiences diminishing returns with anything substantially larger than a Big Pistol.
The Enforcer is a natural evolution of Equalizer pistol technology. It adapts the gyro-stablizers and next generation semi-automatic action into a rugged front-line military sidearm. It lacks the Equalizer's built-in laser sight (and therefore only grants a +1 bonus on Aiming), but makes up for this by all but eliminating recoil. A button on the side of the gun switches it from semi-automatic to fully automatic fire; the recoil-free action gives the shooter a +1 to any Burst Fire roll. The Enforcer uses Pistol ranges, and has a 50-round magazine.

The Plasma Rifle is a powerful and accurate energy weapon. It fires bursts of superheated plasma encased in a powerful magnetic field, which erupt in flame upon hitting a solid object. These bursts, which are about 10 inches in diameter, travel relatively slowly and are easily visible, so attempting to Dodge one has no penalty. Plasma bursts use Rifle ranges, and do 18 points of Fire damage.
While extremely hot when produced, the plasma dissipates and cools very quickly once released. Targets hit by plasma bursts smolder for a few seconds, but only objects that are extremely flammable or covered in an accelerant are likely to catch fire. The technology that generates the plasma bursts and their magnetic containment fields is poorly cooled. As a result the Plasma Rifle has a slow rate of fire compared with most firearms, and may be fired no more than two times per Turn no matter how many actions the user has available. Factory standard Plasma Rifles can fire ten times before they need a new power cell.
The Shock Rifle is an advanced energy weapon which owes as much to the Phase Stream Projector as to the Plasma Rifle. It fires a fast-moving laser-like beam of bluish-white energy which inflicts 18 points of Bash damage. The shooter can also opt to fire a slow-moving ball of energy that inflicts 50 points of Bash damage on a direct hit and 10 points to everything within a 10 foot radius. Attempts to Dodge this energy ball have no penalty, and the Dexterity + Gun Fu roll has a -4 penalty. In either case, anyone or anything affected by the Shock Rifle's attack that is not braced against a solid object must pass a Constitution + Acrobatics roll with a penalty equal to the Success Levels of the attack roll to resist being thrown back one foot per Success Level.
The shock rifle is popular due to its accuracy and ease of use - energy cores plug in below the barrel and can be swapped as one action in combat. A shock rifle can fire 20 times on one core (the alternate firing mode consumes three shots). Shock Rifles use Rifle ranges.
The Phase Stream Projector was originally intended as a vehicle-mounted crowd-control weapon. It fires a continuous beam of greenish energy that the user can direct as needed. The current version of the Projector unit is worn over the user's hand and forearm like a gauntlet, which makes it somewhat unwieldy: the roll to use it is Dexterity and Gun Fu - 2, and the weapon is only accurate within Pistol ranges. The energy stream does 5 points of Bash damage per Turn, and may be held on the target for multiple Turns. Damage from successive Turns is cumulative for purposes of determining Knockdown.
The Projector can fire for up to 60 seconds before it needs to be reloaded. The user can keep her Phase Stream Projector trained on a target by making one attack roll per Turn. However the weapon is still rather clumsy, and any actions taken aside from turning in place or walking calmly will break this aim. The Projector's energy does not noticably affect inanimate objects: walls are not scorched, and glass does not even break from the force.
The ultimate development in stun gun technology. The Van de Graaff Pistol produces a high voltage/low amperage burst of electricity, which arcs from target to target leaving them very dazed. The electrical discharge only works within about three yards, but will affect up to one target per Success Level within a roughly 45 degree arc in front of the user. The user can aim at a particular target, but the secondary effect (who the discharge arcs to next) is totally random. Due to the fundamental principles behind the VDG Pistol, the effect never arcs back to the firer.
The VDG Pistol does no damage, but anyone hit by its effect must succeed at a Willpower + Constitution roll with a penalty equal to the Success Levels in the attack to stay on her feet. Even if she succeeds, she will still be stunned (losing any and all further actions this Turn). The Van de Graaff Pistol requires a Dexterity + Gun Fu roll to use.