You might consider Modx. It is probably the easiest CMS when it comes to integrating your existing site. Some learning required of course, and setting up a blog is more probably more complex than with Wordpress, but your degree of control over the look and feel is unreal - it’s just like an ordinary website.
I’ve used several content management systems for myself and for clients and I have to say Wordpress hands down has been the best. Very little html or css knowledge needed, extremely user friendly, seo friendly and thousands of plugins to support it.
Never used modx, so can’t remark on that software though…I’m sure it’s worth checking out.
I will suggest Stiva Blog Script http://www.stivablog.com -this is perfect for integrating into a clients’ websites - only one line code. It comes with the source code and you can change and modify the script. I think it’s very easy to use as well.
It’s developed by stivasoft, I’ve used these guys for a calendar script customization once and I do not hesitate to recommend their site to you <snip/>. They have useful resources and a lot of nice scripts that would help in a lot of projects.
So you won’t make a bigger and useless effort i recommand you also wordpress. I have a website made on this platform and there are only 4 or 5 stept to follow to post something. You don’t need any HTML and in here you may learn some HTML tricks to change some small formatting design only by using it and imitating.