WordPress is a free downloadable personal publishing application that is a great blogging tool. Apart from the application, there is a library with hundreds of free WP themes from which to choose.
If you want something clean and simple, but colorful, there is Mantra, for example. The layouts, fonts, colors and graphics can all be customized. Using the admin panel you can easily change the background image; header image; content, dimensions and position of the sidebar; text color; paragraph indent and many more things. There are 40 theme options.
If you want something more elegant, but still simple, there is Grey Opaque. This is a very stylish, modern- looking theme in grey with opaque effects. It has a sidebar with two widget areas and other 4-widget areas in the footer. The Twenty Ten theme is also simple with the same 6-widget areas. The menu, header image and background can be customized; it has style sheets for print and categories such as “Asides” and “Posts” which can have special styles.