Modx is quite simple to use once you've read the beginner tuorials, Unify also looks really good, although I have not tried it myself yet.

I am developing a MVC. website and want to implement a CMS system. So far I have seen umbraco, that looks good, but the help is scarce and home video section is empty, and DotNetNuke, which seems to be well again, but I feel it's not for developers, plus much more they need and want.

there are many open source code on the net,. you can google it.

Not for a blog. That is more than a traditional website structure, and I just want the opportunity for clients to edit pages and create new ones. All in a way that can not spoil the design and content they create becomes the XHTML code looks clean and beautiful. Easy to use. For me, during the development and style and the pages while editing.

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Well,CMS Made Simple is designed to keep the code and content separately, so that administrators can manage content without having to know anything about coding.There are many CMS solutions available that seem to do everything except your laundry.

You can create a custom WordPress powered CMS web site with just two sections of code.

I would go with Wordpress for a simple project like you discussed. If you ever have the need to expand, Wordpress can do a little more than what you need as well!

If you want a really cool CMS, I would suggest checking out Drupal (just to see the differences between all of these CMS's being recommended). A lot of people are between Joomla -vs- Drupal so definitely check these out!

how about the site builders offered by different hosting companies? Some of them are known as really good ones.

CMS Made Simple was released in 2004 and is designed to "pretty small sites from a few to several hundred pages. CMS Made Simple is designed to keep the code and content separately, so that administrators can manage content without having to know anything about coding.

Drupal is the best, maybe it’s not that simple but it’s better.