Macha
It is a single-column theme with bold headers and focuses on easy reading. There are no images used, it is SEO optimized, and is perfect for people that don’t want to get bogged down in all of the technicalities of other themes. There is also a widgetized footer with 3 places to put widgets in to help compensate for a lack of a sidebar.
Clear
It is minimalistic one-column theme with the widgets all arranged at the bottom. Clear was designed to make your content stand out and make everything else get out of the way.
Slidette
It comes in 3 colors (green default, blue and black) , with a slideshow and a featured first page 4 posts from a category, two columns and dynamic widgets for the sidebar on the right and in the footer.
I love Clear. That looks like such a good theme. Something I’m not going to use on my WordPress site for the short term, but nice and light and totally appropriate for something like my Tumblr as well.