Named in honor of Johannes Kepler the famous astronomer, Nvidia's next GPU architecture will be arriving in 2011. Most excitingly, it will be built on the 28nm process, in contrast to AMD's soon to be launched 6000 series that will be built on the 40nm process.
Kepler is projected to be over twice as powerful as Fermi (in terms of double precision computation per watt, effectively graphical power).
Continuing in the vein of famous mathematicians, Kepler's successor will be "Maxwell" in honor of James Maxwell, which is slated to arrive in 2013 and is projected to be triple the strength of Kepler. They will be built on the 22nm process, assuming that 22nm is ready to go by then (this generation experienced a delay with the transition between 40nm and 28nm, which won't be worked out until next year).