OutKast - Return Of The G
http://www.youtube.com/watch?v=QXSWwsrSZ9o
It's absolutely amazingly well structured. Blows me away every time.
Andre's verses is split into, almost, stanzas - each stanza switches between a general point on society, followed by one specific to OutKast (mainly attacking the criticism they'd recieved after ATLiens). It's so great because it represents immediately there reasons for the album (Aquemini) in such an amazing juxtaposition of bars.
Then Big Boi's first couple of bars links directly to some of Andre's complaints ("ready to rob, steal and kill"), and he does the same thing as Andre just in a more subtle way, linking the general and specific points so effortlessly you barely even notice it.
It's one of my favourite songs ever, and structurally, my favourite.
Any others?

















Him and Logic together are a Great team