There are too many manufacturers in the galaxy to name them all, but here is a list of the main weapon and armor suppliers to the Citadel.
-Aldrin Labs is a human manufacturer based on the Luna colony. Providing basic, reliable equipment at an affordable cost has made them a primary supplier of armor, omni-tools and bio-amps to the Systems Alliance military. Aldrin Labs also manufactures the hand-held stunners that are mandatory for all Ascension Project staff to carry.
-Ariake Technologies, an Earth-based electronics concern, is best known for their high grade omni-tools. Recently they have branched out to develop a line of high grade armor with an enhanced ablative weave to provide extra protection. Ariake Technologies manufactures Mercenary Armor for humans, krogan, and turians.
-Armax Arsenal is the main supplier of elite turian military units, Armax Arsenal weapons and armor are high quality, high priced and very difficult to acquire for most non-turians. They only manufacture for Turian, and Humans. Armax Arsenal produces a range of hunting bows for large game hunters that work equally well against other targets
-Dah'tan Manufacturing Company is an Asari manufacturer know for making weapons specifically designed for Asari commandos. They operate in Asari space so they operate under standards most humans are uncomfortable with, but they do supply excellent weapons and bio-amps.
-Elkoss Combine is a volus manufacturer based in the Terminus Systems, the Elkoss Combine produces less expensive versions of items carried by high-end manufacturers. Functional yet affordable armor, weapons and omni-tools are all available from the Elkoss Combine.
-Elanus Risk Control Services (ERCS) is a private security corporation that provides a host of services ranging from simple event security to professional mercenary companies and star ships to counter piracy. ERCS began as a privately-owned turian security firm but has since expanded into an interstellar conglomerate after opening itself up to foreign investment. Their affordable yet reliable armor, weapons and omni-tools are popular with security personnel and mercenaries.
-Hahne-Kedar are a reliable and efficient, Earth-based manufacturer and has become a major supplier to the Systems Alliance military. Their weapons are stock quality at best, though they have become popular in select groups.
-Hahne-Kedar Shadow Works was founded a decade ago, this Hahne-Kedar subsidiary is a place for younger employees to "think outside the box". HKSW supplies weapons and armor to Alliance special forces units. In keeping with the parent company's philosophy, products are rugged, reliable, and require less maintenance than competitors. They produce 2 bows, they are expensive but are both prized by anyone wishing to get weapons past security forces.
-Jormangund Technology is the A rising star of post-genophage Krogan industry, Jormangund returns consistent profits through aggressive integration of alien technologies. They specialize in the brutal weapons Krogan desire, good for fighting the beasts on Tuchanka or anyone else a Krogan decides needs a good killing.
-Kassa Fabrication is a human-controlled private company, and is known to make the some of the finest body armor in the galaxy. When it comes to personal protection suits, no expense is spared - as reflected in the exorbitant cost of their products. Kassa also makes top quality weapons such as the advanced Harpoon Sniper Rifle.
-Serrice Council is an asari consortium, the Serrice Council is the creator of the most powerful bio-amp on the market. Not just concerned with profit, they typically make customers undergo a rigorous screening process before being approved to purchase their products. Serrice Council amps are incredibly rare—and highly prized—items on the galactic market.