I came accross this tool Advanced Theme Construction Kit (ATCK) today and I really like it.

It is very useful if you want to build grid layout. i had tried using YUI CSS grid layout directly before. YUI is good, but it wasn't very straightforward if I want to build complex nested grid layouts. But this, with its builder tool, make creating grid easy and comfortable. Nice and clear documents too. Two thumbs up.

Also, if you use Drupal, you can find it as a Drupal module in http://drupal.org/project/atck.