A & E Engineering: Some advanced propulsion concepts described.
Beginner's Guide to Propulsion: Tutorial slides on basic propulsion concepts.
Chemical Propulsion Information Agency: Comprehensive site with technical resources, propulsion papers, meetings and events calendar.
Compreactive Propeller (Airscrew).: It is suggested to use the internal space (internal channel) of a rotating blade as a centrifugal flow pump delivering pressurized air in a jet engine located on the blade tip.
Journal of Propulsion and Power: Site contains a searchable Table of contents and information for authors and subscribers.
Propulsion Directorate, Air Force Research Laboratory: Information on their research projects, and a propulsion primer
Rocket Science Institute: Offers texts about rocket propulsion and propellants, from black powder pyrotechnics to NASA-scale systems.