Good UI is a rather subjective matter and one based on design techniques rather than technical XPages code. There are a number of XPages applications available to the web, such as xpages.info. Searching for ".xsp" should return some. But, as I say, good UI design goes beyond XPages to web design. The whole topic is too large to cover in a forum.
For OneUI documentation, look at the Lotus Domino App Dev wiki http://www-10.lotus.com/ldd/ddwiki.nsf/dx/12102009164524SCALK8.htm. Bear in mind the documentation is not XPages-specific but cross-platform.
In terms of using OneUI in XPages, the Extension Library offers a number of controls such as the Application Layout control. There is a whole chapter in the XPages Extension Library book on that control, again, too much to paraphrase on a forum.