Keep in mind that you can use any BB30 or PF30 cross frame with one of these http://beercomponents.com/ . They are cross tested and approved.
D'oh! Didn't see this post.
A few to choose from:
Chilli Con Crosso 2011 (Not a SSCX frame but converts) - http://salsacycles.com/bikes/chili_con_crosso/
Specialized Tricross Singlecross (ebay)
Kona Major One - http://www.konaworld.co/bike.cfm?content=majorone
Conquest Pro SS Frame - http://www.redlinebicycles.com/bikes/cyclocross/2012-conquest-pro-s...
Masi Speciale CX/SS - http://www.masibikes.com/bikes/competition/cx-ss-2012
2012 Civilian Le Roi Le Veut -http://www.competitivecyclist.com/frame/2012-civilian-le-roi-le-veu...
Some of the above you can find as full bikes or frame-only. I try to keep a list here: http://sscx.me/pages/single-speed-cyclocross-bikes
I updated the list recently:
Not a maker of frames or bikes, but BEER Components makes a BB30 EBBthat will turn many high end carbon and aluminum CX frames into single speeds.
Been using one on my Cannondale Flash29 MTB, and it's been great. Planning on getting another if I decide to buy the TJX frameset we have hanging from the rafters at work...