Vertex

This theme is one of the best themes I’ve come across in a long time. Cleverly enginerred and designed to work out of box without plugins. I’ve been working with wordpress since version 1.8 and I can tell you for a fact that this theme is my absolute favorite ever. On top of all that it is astonishingly lightweight, specially for today standards where most themes require that you pump up the memory limits on your server, this one, works out of the box with any regular server without tweaking memory limits, timeouts or any of that.
The author also provides a very easy to follow video tutorial, that gets you up and running in no time. This theme achieves the original purpose of the wordpress platform, which is to provide an elegant, efficient and lightweight cms.