Brands

Tokyo Marui
They make excellent guns but are priced extremely high. For a gun with 350FPS you can pay hundreds of dollars. They are supposed to be second to only Classic Army. Their guns are made with steek for realism.
Classic Army
They make the best guns according to what I hear. They are also priced high but their weapons have high performance and reliability. Their guns are made with steel plating for realism.
ICS: Another one of the big three airsoft brands. They produce guns on par with Tokyo Marui and Classic army, and are in the same price range.
Crosman
The Largest distributor of airsoft-related items in North America. They produce ammo, and a wide spectrum of guns from shit to good quality weapons. Check out the Pulse series of AEG's.
Double Eagle
These weapons tend to be somewhat mediocre from my research and personal experience. I have not seen high quality products, they produce low-cost low quality guns.
Jin Gong
Its a chinese brand that makes often unreliable products. Many of their guns are rated unreliable and are not give warranties by the retailer. This company tries to make alternative guns to Classic Army or Tokyo Marui, but failes in both fame and reliability.
CYMA
Like Jin Gong, they try to make high power alternatives to Classic Army and Tokyo Marui, but also fail. They are a cheap chinese manufacturer. They are one of the ebst chinese manufacturers though.
Both Elephant(BE)This Brand is low quality shit.