I remember a few years ago -- about 1999, 2000? -- when The Center for Progressive Christianity (and particularly their Eight Points) was all the rage in UU Christian circles. I don't hear nearly as much interest now -- I don't hear as much griping about the Principles and Purposes either, so perhaps my sampling mechanism is at fault -- but I've kept my ears open for other formulations that others might find useful.
So what about the Statement of Faith of the United Church of Christ, and particularly the newer "doxological" version? I'm sure its origins and use as a denominational document has kept it underrecognized, but it should get a wider hearing, especially since it is old enough to have its own literature and critique.