Both OBS and LBS, NYCBikes in Brooklyn at www.nycbikes.com. Knowledgeable, fun shop, great stock, and prices on my wheelset were cometitive with eBay stores (who btw aren't there to true up your wheels after the first couple of weeks of pounding the !*@&* out of them in the city). Here's a step by step description of how Will helped me build mine: http://www.jaycokingpin.com/singlefix.pdf

A buddy bought his Cityfixed (about a 600-700 dollar bike) and loves it, if you're not into the the do it yourself thing. In fact he liked it enough to buy his wife a Tricity (sorta the same frame only with a 3 speed internal hub--no fixed gears but then again she hauls their kid back and forth across the Williamsburg bridge in the baby seat).

All for what its worth. Cheers...