<a href="http://github.com/jbalogh/zamboni" rel="nofollow">http://github.com/jbalogh/zamboni</a> would probably be a good start, and <a href="http://pinaxproject.com/" rel="nofollow">http://pinaxproject.com/</a> another.
How can you judge the architectural design of a Django project just by looking at a site's interface? Do you mean clean URLs? Or are you asking for open source projects, like @madhouse referred to, which were built well?<p>Both of my projects: <a href="http://www.littleheroes.com" rel="nofollow">http://www.littleheroes.com</a> and <a href="http://www.repustate.com" rel="nofollow">http://www.repustate.com</a> are Django projects and in my biased opinion, they're laid out well under the hood.