hmmm... 26.8...

I currently have two bikes (it'll be three, once the Panasonic comes back from the builders) that take 26.8, although they each have quite different tubesets...

My lugged '93 Bridgestone XO-3 is made from tri-butted Ishiwata EXT. It's supposed to be 27.0, but 26.8 actually fits much better...
My Torelli (a '97, I think) is Columbus Aelle; like the Bridgestone, the company spec'ed the frame for 27.0, but 26.8 is a perfect fit.

My '91 Trek 820 is straight-gauge Trek 4130, and actually takes a 26.2; I've had plenty of trouble finding a good seatpost for it (this is where I learned my lesson; ergo why I'm having my Panasonic modified).

The rest are all 27.2.