It is somewhat embarassing when you write a tutorial which reminds you how frequently you break the "rules" yourself. That happened to me earlier this week when I wrote a short article about site usability, so I decided to design a new WordPress theme which breaks fewer of those rules.
It is a 3-column fluid design (ie it adapts to the visitor's screen resolution). Changing the header image requires nothing more than over-writing the current jpg file with another. Further styling changes should be easy enough for anyone with a modest knowledge of CSS.
"Olives" is coded in validated XHTML strict and it's FREE!
http://carpejugular.com/olives-a-free-wordpress-theme/