Lets see what I can remember..
Okay the Locust are big on numbers to the point that the 'Destroyed Beauty' artbook says that while they lay ambushes, use cover, etc. they're perfectly willing to sacrifice hundreds of drones to kill one entrenched Gear.
Locust drones themselves are extremely tough, able to fight in little to no armor on an equal footing with the heavily armored Cog troops and even in the cinematic trailers it takes long bursts to down locust troops. Most drones clock in at 2+ meters and ~120 kilos and the Destroyed Beauty artbook's author (a COG Gear) says he's never seen one lose morale and break.
Most locust drones carry the 'Hammerburst' which judging from the design I'm guessing is an SMG. Unknown caliber but it fires a pretty big round in three round bursts.
Concept art image. Note the size of the shells and bore. Groups of three drones known as Troika Cabals make use of a Troika HMG which according to the Destroyed Beauty artbook 'Makes our .50 cals look like pea-shooters'. Drones have also been known to carry Gnasher shotguns (able to blow apart an armored gear or locust drone at point blank range), bola grenades, Longshot Sniper rifles (large caliber, bolt action). IIRC they've also been known to carry stolen Lancer assault rifles.
Theron Guards are essentially better trained drones with body armor. Known to carry the 'Torque Bow', a motorized bolt thrower that fires off explosive bolts that stick in a target and detonate. They also carry the usual locust weapons presumably.
Boomers are massive locust warriors who carry the Boomshot grenade launcher and take prodigious amounts of ammo to bring down.
Another inhabitant of the Locust tunnels are the Kryll, swarms of ravenous flying creatures that are rather like the swarm of little baby monsters from Pitch Black. They don't like light though to the point where a person standing in a firelight is safe from them as long as the lights stay on. They will however descend upon anything Locust or Human that steps out of the light and tear it to pieces (the exception to this being General Raam who commands a swarm of them). Not much of a direct military threat so much as an extreme hazard at night in the areas where they swarm.
Berserkers are female drones. Blind they rely on sound and smell to locate their prey and proceed to bash the living hell out of it until it dies. Bull charging berserkers have been known to crash effortlessly through stone walls and pillars though a tough enough obstacle will stagger them and live them momentarily disoriented. Immune to fire from most standard COG weaponry neccesitating the use of the Hammer of Dawn to weaken them to the point that regular rounds can penetrate (though the external damage heals quickly rendering the berserker once more immune to normal weapons fire).
Corpsers are gigantic spidery monsters the Locust use to dig large tunnels and emergence holes. They're also apperantly fond of cat-and-mouse games with their prey judging from the dialogue in Chapter 2 of the game. Attacks by undermining things and using it's massive claws and breath weapon.
Wretches are small locust usually used as cannon-fodder. They cling to walls and ceilings, drop out of vents,etc. No weapons they charge and leap into hand-to-hand to do all their damage. They do however die far more easily than other Locust. Some Wretches have been directly consuming Imulsion giving the pitch black skin with glowing eyes and mouths. These wretches attack in the usual manner only now they explode when shot, hit, or otherwise jostled too hard.
Brumaks are the Locust's tank equivalent, a massive beast with a drone handler and with bunches of assorted weaponry and armor strapped to it.
Seeders are essentially Locust anti-aircraft minelayers. They're immune to standard weapons (needing the Hammer of Dawn in the game to take them out). They also jam radio communications in the area around them and attack by releasing Nemacyst spore mines, kamikaze creatures that float about rather lazily, sometimes even concealing themselves from view, then accelerate rapidly to ram and detonate. (It should be noted that in-game they move much slower than they do in cut-scenes). They can also attack ground targets though not just stuff in the air.
That's pretty much everything I can remember running into or hearing about.