Crayon World is a clean theme with a colorful header.

Prebuilt is a simple red and white theme for WordPress. It has a top menu bar, relatively wide right side bar and an extended footer with Flickr integration.

From the site:

Prebuilt was created not to be heavily graphical and feature a lot of ajax goodness, but to be effective while at the same time, an easy way of learning Wordpress.

From the site:

Ambiru is a calm, reassuring theme developed for WordPress.

Ambiru is an unique single column theme with a header image.

Gespaa is a single column blue gray theme.

From the site:

Gespaa is an attractive, smart theme that was originally designed for private use on this very blog.