I think wordpress is perfect for that kind of thing. It does run on .php, but all the styling and everything is based on css and HTML. I don't know much about .php, but I've created a lot of wp themes, it works great as a CMS. This goes over everything you'd need to know about creating a custom theme (in pretty simple, step by step terms), if you feel like some heavy reading: http://www.wpdesigner.com/2007/02/19/so-you-want-to-create-wordpress-themes-huh/

And yeah, once the themes all set up, all the client has to do is click "add new post"

Thanks so much cutty, did you end up using wordpress as the complete solution or integrating it into a website that was pre-existing? I'm hoping to be able to code the website completely then just drop in something like wordpress into a div box and be done to keep it simple, but maybe it isn't going to be that easy.

Matt Borchert said:Thanks so much cutty, did you end up using wordpress as the complete solution or integrating it into a website that was pre-existing? I'm hoping to be able to code the website completely then just drop in something like wordpress into a div box and be done to keep it simple, but maybe it isn't going to be that easy.

Its do-able but I think its going to take a little php to pull off.
*Note: This is just off the top of my head so take it with a grain of salt*
Create the site separate to wp. Then put wp inside a folder in the root directory so you have something like www.mysite.com/blog/wp-article.
You can then use a little bit of straight php on your sites main page to access the posts table in the database that wp uses.
ie: (sudo code)
$q = mysql_query('SELECT * FROM wp_posts WHERE ...stuff that you want ');
while($r = mysql_fetch_assoc($q)){
echo $r['post_title'];
...
}

http://www.burnseo.com/blog/2009/10/23/integrate-wordpress-into-existing-website-tutorial/

if you aren't married to wordpress, you can embed tumblr into a .html page with a single line embed code and than a few css tweaks to make it look right.