This is a great article on that very subject. I've send it to many clients.
Google is powerful, don't piss her off
http://www.fixingyourwebsite.com/googleisgod.html
"Other people said 'Making your site look good in Lynx is like accessibility. I'm not selling to the blind so why should I go to the trouble of making my site accessible?' Why? Because the most powerful Internet force known to man visits your web pages like blind people and folks who use Lynx - Google."
I've collected other ones that I've found helpful here
http://www.finalsigma.com/web-writing.html
Would you guys like to suggest some others that you've found helpful?
EDIT: I'm not plugging my own articles. They are just ones that I've found useful.