Village Instruments is working on an external Thunderbolt PCI Express graphics card enclosure, dubbed the ViDock Thunderbolt. This is very good news for anyone with a base MBP 15" or below, or a MBA. The GPU is probably the weakest link on these machines so an external GPU should extend the lifespan considerably. Now I won't feel as bad when they (likely) release the Macbook Air Pro later this year.
http://www.engadget.com/2011/08/04/external-thunderbolt-graphics-card-for-macs-to-be-developed-soon/
http://www.engadget.com/2011/08/04/external-thunderbolt-graphics-card-for-macs-to-be-developed-soon/