theming

The Semantic Views module for Drupal 6 allows you to easily insert HTML markup for your Views rows and fields.

The Contact form blocks module makes your site-wide contact forms available as Drupal Blocks.

Composite Layout allows your nodes to be displayed in complex layouts. Currently, two and three column layouts are provided. You can also add other nodes, blocks, and even CCK fields to your node's layout. The content area of your node is divided into zones and you decide what should appear in those zones. Zones are essentially the same as Drupal blocks, but they apply to nodes rather than the entire site.

You can think of Composite Layout as Drupal blocks for nodes.

Custom Page is an advanced theming tool, allowing developers to easily create pages with custom templates and maintain full control over the output (e.g. HTML).