I'm thinking of pairing a modern fixed-gear with a vintage road bike (preferably with an internal gear hub, but man are those hard to find!).
I've been looking at the Jamis Beatnick and the SE Lager as a "school and back" bike.
For the vintage bike, I've been looking for Raleighs, etc, from the 1940s and 1950s, but apparently they're very rare. I might have to give up on the internal gear hope (short of doing a conversion myself) and go with a vintage 10 speed or similar.
Another option would be to flip it: get a vintage fixed gear (tons of those around) and a modern road/comfort bike. I like the first setup though.