Specific Impulse of various types of Rocket Engines    

Engine Type            Specific Impulse (sec)

   Chemical                150-450
Nuclear Thermal            825-925
ARCJET (Electrothermal)    800-1200
MPD (Electromagnetic)      2000-5000
ION (Electrostatic)        3500-10000

Source : "Strategies for Mars", Chapter 8, "Pathways to Mars" by John C. Niehoff and Stephen J. Hoffman