Bilstein is a well known brand regarding dampers and complete suspension systems.
KW is for sure one of the biggest and best suspension supplier in the world. KW Suspensions is offering different types of coil over systems, with or without adjustable bump and rebound set up, for road use, track days or even highest competition level. They can also supply accessories like camber plates, help springs etc
H&R is offering lowering kits and anti roll bars systems.
ST Suspensions is actually a sub brand of KW Suspensions ST Suspensions is offering different types of suspensions from a set lowering springs to fixed or adjustable ride height suspensions.