One of the nicest free WordPress themes I have found recently is Absolum. it is a really cheerful clear theme, that can turn a dull looking site into something that looks interesting and fun.
Absolum is produced by the good folk at Theme4Press. Although it looks very simple, it offers a wide range of options once you have it installed.
One of the features I most like is the very well formatted implementation of the WP Gallery feature which allows you to preview images and add captions.
On top of this, the theme allows you to switch the sidebar from the right to left, or disable it altogether. You have a choice of four subsrciber buttons, and can choose between many fonts, There is a complete customisable menu, and six areas for widgets, and also a theme visual editor.
All in all, this is a great theme, that reminds me somewhat of the early and not so complicated versions of Thesis, but it looks better.
Click here for a live site using the Absolum theme.