E3D
e3d-online.com
UK maker of hotends and extruders, best known for the V6 (a long-time standard) and the Revo, with tool-free quick-swap nozzles. E3D also created the ToolChanger platform.
Slice Engineering
sliceengineering.com
Gainesville, Florida maker of high-performance hotends, including the Mosquito and Copperhead, plus high-temperature thermistors and other parts.