On Plasma Propulsion

It turns out that the plasma cannon we were envisioning at our last meeting is pretty similar to a VASIMIR engine - notice the use of radio waves (similar to microwaves) to excite the plasma:
http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket

General definition of plasma propulsion engine:
http://en.wikipedia.org/wiki/Plasma_propulsion_engine

Also, here are is an excellent paper on plasma propulsion - it has some other interesting ideas like using the magnetosphere for propulsion, and creating a mini-magnetosphere on spacecraft to protect from radiatio/cosmic rays, etc:
http://www.electrofluidsystems.com/news/DGLR-2003-257.pdf

And then there's this recent story that's been going around, which Travis pointed out: http://www.livescience.com/technology/080612-plasma-saucer.html

Also, here is an interesting site about using LTA (Lighter Than Air) technology to get to orbit, using a three step approach - A robust V-shaped wing craft to get to a floating station at 140k ft, where a lighter and more delicate (and streamlined) V-shaped wing craft with ion engines to slowly get to orbit in 5 days. It's a little hard to glean too much from their website, I had to buy their book "Floating to Orbit" to figure out what they were really up to:
http://www.jpaerospace.com/