Free WordPress Themes at the WPShout theme house
Here you'll find free WordPress themes.
They're all relatively simple, allowing you to make them as complex as you want with plugins etc.
If you're looking for something more advanced then hop along to WPShift where they've got themes that you can literally build by dragging and dropping. You can really easily customise them, too!

Free WordPress Theme: Nothing Much
Nothing Much is a free WordPress theme especially made for WPShout readers! It’s a super minimalist, single column, simple WordPress theme that’s the first to join WPShout’s new Theme House. Image-less and only two files small, Nothing Much loads in a flash and would look great in use on a personal blog.
