Since the last batch of search engine friendly WordPress theme recommendations went over so well, here are five more themes for the full version of WordPress (and if you’re on WordPress.com, don’t despair; we’re in the process of reviewing the included themes right now and will publish our recommendations for you soon).
XV - Revised
We like this theme’s code because it:

validates
has better-than-average code structure
emphasizes your post titles
emphasizes your blog name
emphasizes your blog’s description
uses unique page titles

Many people have been reading the posts on ProBlogger and this blog about the importance of good theme code and the role it plays in your search engine traffic.

Now, I’m a little biased , but I think one of the best ways to get a great theme with great code is to have it built that way; you get the best of both worlds: a custom theme that represents you perfectly, and great, search-engine-friendly code.

However, I’m also a realist, and know that many bloggers can’t/don’t want to put cash into their blogs, so I wanted to take this opportunity to highlight some beautiful WordPress themes that also feature excellent, search-engine-friendly code. Read on to see the first five selections (in no particular order). (Hold your mouse over a “reason” to see a slightly longer explanation.)