Googling around tonight, I discovered UKUnitarian.org.uk "A resource about, and for, Unitarians" -- and a wise, common use of a branded Web resource for (as yet) 31 mostly-small congregations and institutions. Plus, it's a free service for the churches and simply-formatted sites are bright, cheerful and both better than nothing and better than something over-adventuresome that would be hard to maintain.
But even more than this, UKUnitarians.org.uk has a map mashup with Google Maps, pinpointing every Unitarian and Free Christian Church in Great Britain (and a handful in Ireland.) A link to congregational Web sites would be nice, but I oughtn't be greedy.
Good stuff; a United States version would also be a great idea.