Check out this theme from PixelUnion!

The most popular theme on Tumblr just got even better! Fluid 2 is packed with a heavy feature set, including an HTML5 media player, photosets that “dim the lights,” endless scrolling, keyboard shortcuts, and customizable everything. Plus, the archive, Ask, Submit, Twitter, and blog information are organized in a neat little toolbar at the bottom of every page.

Try out the demo and use it on your blog for just $49.