Yesterday I committed a first version of my new Drupal theme FriendsElectric. It is PHPTemplate-based and tableless, uses semantic XHTML and fully supports all theme options (slogan, logo, primary/secondary links, etc). You can check out a quick live demo on my site. The theme is designed for compatibility with the latest versions of the major browsers out there, but will not work on dinosaur browsers (most notably, IE5/Win and IE5/Mac).
The theme was mainly created to answer the repetitive questions about Drupal.org's own theme, Bluebeach. FriendsElectric is similar to Bluebeach under the hood, but is different visually. I've also kept a short log about the development of the theme which I intend to write out properly and put online when time permits. FriendsElectric will be used to illustrate various issues in my DrupalCon presentation about Theme development.
However, this is not just an example theme, I've tried to ensure it's one the highest-quality themes out there, with clever stylings for sidebar lists/menus, new comments, form items, blockquotes and more.
I noticed that most of the Bluebeach questions were about CSS and not about Drupal-specific issues. It is not my intention to teach people HTML/CSS, but simply show what particular things you need to worry about when theming Drupal. For the rest, refer to CSS-specialized sites like: