This guy is pretty impressive.

http://industrial-organic.net/

http://www.ashbydesign.com/

(disclaimer: Neil was one of my design teachers, the guy who did the site is another )

There are a couple of good discussions on Speak Up about this topic, with plentiful comments and examples...

Number 1, dating from 2004, and the more recent Number 2, from this year.

Design Chapel

Diversity is great, provided it demonstrates a consistent design vocabulary, or something like that.

Sometimes a portfolio should be about showing the full breadth and depth of your abilities, but more often it is to present a sufficiently reliable vision that a potential customer can point to it and say "I want something like that".

I was not intentionally stating that the best portfolios are always diverse, though it read like that in relation to the topic. I've now edited the link :)