I want a jet-trike though, as I'm slightly less likely to become a stain on the tarmac that way.
Two small jet engines, one above each rear wheel - that way reverse thrust assisted braking becomes possible without frying your back.
Some independant control of each engine (automatic using a microcontroller, as I don't want a nasty control surface), and possibly mechanically vectored thrust linked to the steering to give better cornering.

I've put too much thought into this.
The problem with jet propulsion is that you get very poor acceleration at low speed.