Our lugged road frame the Stanyan will swallow 650Bx38mm tires with room for fenders. Back when it was still called the speedster Ed 650Bradly over at bikeman.com built one up with 650Bs. even thoguh it was from all the way back in 2007 I still love to look at this build. So nice.
You can fit 650b wheels on every size of the Buena Vista mixte. Here's on built up by the intrepid 650bers at FreeRange Cycles in Seattle.
People have also sucessufly converted the Doublecross DC and the ES to 650b. And of course the smaller sizes of the San Marco are build specifically for 650b wheels.
These tire are great for when you want a little more cush on your ride, but you're not necessarily going offroading. There are a number of great 650b options on the market now, in including the Soma New Xpress and B-Line (soon to be available in Terracotta), and the Parimoto from Pacenti. They can be found here http://store.somafab.com/tires1.html or at your local bike shop.