Why not stick with Planet X? Their carbon frames are pretty swish.
Failing that, Bianchi makes some nice frames at decent prices. But then there are billions of options out there. Have a look at
Opus too - small company, great frames. I've got an Allegro and it's lovely. Even if a company doesn't list individual framesets on their site, they can almost always be had on special order.
GVH Bikes has a varying and often rather eclectic selection of frames as well. Same with
The Pros' Stuff.