How Stuff Works: How Fusion Propulsion Will Work - Shows how building a fusion-powered spacecraft would be equivalent of developing a car on Earth that can travel twice as fast as any car with a fuel efficiency of 7,000 miles per gallon.
Innovative Nuclear Space Power and Propulsion Institute - Researching square lattice honeycomb ternary carbide fuels and nuclear electric propulsion based on gaseous and liquid fuel reactors with magnetohydrodynamic power generation systems.
NERVA - The Nuclear Engines for Rocket Vehicle Applications project. Started by the Atomic Energy Commission and NASA in 1961 and cancelled in 1971 due to radiation worries and a lack of interest from NASA.