Centrospazio: A space technology research laboratory specialized in Electric Propulsion development and testing: Hall thrusters, FEEP systems, MPD thrusters, arcjets.
Electric Propulsion: Research carried out by Stanford University on electric propulsion systems.
Electric Propulsion and Plasma Dynamics Laboratory: Research in electric propulsion, plasma thrusters and fundamental problems in plasma physics. Princeton University.
Electric Space Propulsion: Research carried out by the Institute of Space Systems. Also contains a good overview of the various types of electric propulsion.
Electric Spacecraft, Inc.: A network for researchers of electrodynamic field propulsion techniques for space travel.
Hall Thruster Experiment: Princeton Plasma Physics Laboratory. This site documents the undergoing research in electric propulsions.
How Electromagnetic Propulsion Will Work: Illustrated tutorial shows how Goodwin's electromagnetic-propulsion system works and how it could send spacecraft deep into space.
Interstellar Transportation and Exploration: General concepts and preliminary design for electrostatic propulsion system with goal of reaching 0.2 to 0.5c for interstellar voyages.
Ion Propulsion FAQ: A beginner's overview of ion propulsion.
Mini-Magnetospheric Plasma Propulsion: An advanced plasma propulsion system that will create a large scale magnetic bubble around the spacecraft to ride the solar winds.
Solar-Electric Ion Propulsion: One of the 12 advanced technologies that was validated by DS1 during flight.
Tethers Unlimited: Use of space tethers for propellantless electrodynamic tether propulsion, pumped tether length propulsion, and transferring energy and momentum from one spacecraft to another.
UMich Plasmadynamics & Electric Propulsion Laboratory (PEPL): Researching electric space propulsion with the goal of increased efficiency and better understanding of spacecraft integration issues.
Variable Specific Impulse Magnetoplasma Rocket (VASIMR): Description of one of the propulsion systems being considered by NASA for a manned Mars mission.
Xenon Ion Propulsion: Description of Boeing's commercial XIPS (Xenon Ion Propulsion System). Designed for satellites, but a specialized version of it was used on NASA's Deep Space 1 spacecraft.