Yahoo have updated their excellent pattern and library resource with a couple of interesting things (css reset, hierarchical menus, css fonts), but the one I'm going to mention is CSS Grids. This is a CSS file which, when you give your HTML the correct structure, will give you a robust two column layout. Separated into inner and outer templates, the outer providing the columnar structure and the inner being a grid within the content column of the outer template. Here's a good example of the CSS Grid idea - the secondary column is a sidebar, and the main content column contains a grid of four other columns.
The strength of this release is that it will be consistant - the CSS will be rock solid. It's a good jump-off point for developers to produce robust layouts, letting them concentrate on the finer points.