I know Deb W set her bike up to accept either 26" or 650C wheels, but it depends on what brakes you have if they can be adjusted (her bike was custom built with this idea in mind). Also, how much clearance is available on the brake bridge and fork also effects what tire sizes you can run regardless of wheel size.

I have a velocity uriel set that came on my terry isis that I think are fine, and also a 650c set of easton circuits that came on my cervelo RS that I really like. I like the circuits more cuz they are lighter, but never had any problems with the velocity set. I think the circuits have been replaced by the EA70. None of these are fancy shmancy wheels though, I've heard the eastona described as high value though, good light wheels that aren't too expensive.