BloggingPro has a great rundown of the newest theme files introduced in the latest version of WordPress. Here’s the short list:

• The category-slug.php template: Before, theme authors were limited to using category dependent theme files that used the category ID. In WP 2.9, category slugs can now be used in the category ID’s place. That’s a 100% more descriptive and convenient than the old way.
• The tag-id.php template: Tag-based templates are now available too. Although it suffers the same old problem as the category-id.php template. Maybe we’ll have to wait for several more WP version updates for that to be addressed.
• The page-slug.php and page-id.php templates: Page-based templates complete the circle. Now you can also style specific pages based on either its ID or slug.

While we’re on the topic of custom theme files, let’s talk about the old but still useful theme features applicable to sidebars:

Sidebar templates, introduced in version 2.5, can create lots of sidebars files other than sidebar.php itself, and call it via the parameter in the the get_sidebar() function. For example, if you want to include a right sidebar called sidebar-right.php, just use get_sidebar('right') instead of the include() function.

Now that you know all about these custom theme file features, you’re ready to create WordPress themes that are smarter and more powerful than ever!