The WordPress users know that all you have to do to change the appearance of a blog powered by wordpress is change its template or theme. Everybody can create a theme, but everybody has not enough knowledge to do it. This is one of the reasons to have many free downloables themes on the web. There are many examples in the official WordPress Theme page.
After download it, you have to install it, but it’s very easy. Place the theme in the wordpress theme directory ( /yourblogspath/wp-content/themes/ ), go to Presentation tab in the admin panel and finally select there your theme.
I like WordPress and I like developing WordPress Themes, so here you have a list of the themes I have made. They are free and you can download theme clicking in the image. Enjoy it!