Well, I dunno why, but I decided to list some of the cool weapon types I figure will be possible in the future. Or at least dream about. The scary part is, with enough money, I could build a lot of these systems from scratch. The ones I could do so with will have an asterisk after their listing. Ones we already have versions of will have a ~.

Kinetic Energy: Using rapid stimulation of certain pieces of matter's molecular and atomic structure to make a controllable (and very small) kinetic field, we could make a weapon that pretty much just makes whatever it hits fry itself. The individual molecules will either move so fast that the friction burns everything up, or the atomic bonds will pull themsleves apart, disintegrating the target.
In the fictional space universe I usually use (not the Mechanoids one, though there are Mechanoids in it) Kinetic energy weapons are quite commonly used, though usually restricted to military and paramilitary use. Larger versions are used as vehicular weapons*~

Kinetic Energy Piercers: We already have something like this. Depleted Uranium bullets that can tear through pretty much anything if given enough kick, but give off radiation and toxic dust when fired or burnt. But imagine if the kinetic energy were used to take, compound, and solidify any material within the energy field (which like I said, must be small, about the size of a bullet) turn it into a projectile, stimulate with said kinetic energy, and fire it. It's like a superbullet, perfect for snipers, and one of the few weapons here that can have its sound and flash reduced.
In my fictional universe, these are the simplest kind of firearm (aside from flechette, canister, splash laser, and charge bullets) available outside a museum. They are commonly used for hunting.*~

Splash Laser: This is something I came up with long ago. This weapon works sort of like a gun, but with an added process. The titanium (probably the only alloy that would work for this and be cheap enough to make bullets with) bullets would be stored in a clip that had a second bit for laser gasses. The bullets are fired, then go through a tube that supercools them while adding the laser gasses (freezing the gasses to the bullets) then superheats them and focuses them (activating the laser gasses and melting the bullet) out the end towards the enemy. The result is beyond white-hot titanium and a laser beam smacking into the target (plus residual energy absorbed into the bullets, causing them to fire more lasers into the target when they impact) and roasting them within miliseconds of coming near. Ouch. The issue is how big the cooling system would need to be, because all the heat resistant metals I know of would shatter if used to fire a bullet.
In my fictional universe, splash lasers were supersized and used on spacecraft. By the time a cooling system small and effective enough to be used on hand held splash lasers, the more effective shuriken guns were made.*

Shuriken Gun: Using a system similair to the splash laser, but shaping the round into a buzzsaw shape (and using a stronger, more conductive, fictional metal known as Sverite (pronounced zerite) though it could be done with Titanium) and eliminating any laser energy not stored in the buzzsaw when it is fired. The result is a superheated buzzsaw blade cutting your enemy in half, and simaltaneously cauterzing the wound and ripping the cauterized flesh off with the following focused shockwave.
In my fictional universe, shuriken guns have long since adapted since the Mechanoid Wars centuries ago. They serve in law enforcement groups and lesser militaries as a cheap and effective alternative to charge bullets and energy weapons.*

Canister Round: Similair to something we have today, future canister rounds are pretty much sabot grenades powered by (you guessed it, a laser!) and fitted with a hollow point AP tip. And for all the devastation they cause to their victim's flesh (and anyone nearby's hearing, they are LOUD!), they are commonly up for commercial sale to civilians in my fictional universe, like most solid-shot weapons.*~

Charge Rounds: Made from a fictional, highly conductive (yes, in heat and electricity, but not magnetism yellow and green metal known simply as 'charge', these bullets are really shaped like oversized BBs. They glow bright green and leave a perfectly straight line of little yellow dots behind them. Charge rounds make no recoil, and go perfectly straight unless something is there to affect them. They make a small (about fist sized) but extremely powerful explosion. Strangely, charge will only fire if used in a strange, bolt action like activation system, so most weapons that fire charge look like WW1 and WW2 rifles.

Flecgette: Yes, yes, I know, we already have a flechette sniper rifle, and a flechetter cannon, AND flechette rockets, but this version is BETTER! We all know what flechette guns do. They shoot a little shotgun-shell-type-dealiewhacker that doesn't explode until it gets close to the enemy, and fires darts instead of pellets, and is like someone took ten 12 gauge shells, put them into the target's body, and set them off with a grenade. However, they need to be laser guided and have their little computer recalculated after very shot. My version is (again) laser powered AND guided, and only needs to be set once. You set the laser distance, and the flechette itself becomes a miniature homing rocket that follows the laser signal to the target, receives the command to explode at the base distance set, and explodes before reaching whatever you shot at. It also explodes on contact if the signal is lost, and can be told to go through windows and THEN explode since lasers go through glass.
In my fictional universe, flechette guns (even flechette lasers) are everywhere just because I like them a lot.*~

Phasers: No SciFi universe is complete without these super-powered and renamed lasers (no, I'm not a trekky, I'm a Star Wars fan, Star Trek has too many different story lines to follow) that are also called blasters, hand lasers, beam-guns, and zapps. They take the form of either short bursts of galvanized energy, or super-powered-mega-focused laser beams that cut a swath through the enemy.
In my fictional universe, these are used a buttload. I mean, this pretty much covers all laser energy weapons right here!*

Antimatter: Admittedly, I have no idea how containing them would be even remotely possible seeing as how the only catalyst known to keep antimatter from destroying all regular matter it touches is, well, a buttload of black holes pulling each atom in a different direction. However, how it would work is simple, examplified by the equation: antimatter+normal matter=ZORP! Hey, everythings noexistent! The colision of antimatter and normal matter is the only thing I can really think of right now (though I remember thinking of other things that could...) that can break the law of conversation of mass and eliminate matter and energy. So an antimatter missile would pretty much erase a tiny little piece of universe. However, it also destablizes the universe and speeds up the process by which all the matter in our universe will eventually be all of the same element, and though this, how without anything providing the extra energy and elements neede to expand will cause the universe to turn this excess energy towards collapsing in on itself and emptying half of our dimension (each dimension has two universe, just two, it's been proven by my worst enemies, quantum physicists). It is for this reason taht the mere arming of antimatter weapons is considered a war crime against everyone in my fictional universe.

Im starting to run out of room, so I'll just write this down on notepad and post the rest later. Bye.