By all accounts the Bostick and Sullivan frames are quite nice. They are an APUG sponsor, and their link can be found on the sponsor page. Also, I have heard good things about the frames made by Daniel Pelland, of Pelland Photo. I'm sure there are others.
I use contact frames of my own design and construction. I have been meaning to make a few, and offer them for sale in the APUG classifieds, but it has been too cold to work in my shop.