Wordpress’ conditional tags are by far one of the most useful and unglorified tools for theme and plugin development. Here’s a list of all the tags.
The Conditional Tags can be used in your Template files to change what content is displayed and how that content is displayed on a particular page depending on what conditions that page matches. For example, you might want to display a snippet of text above the series of posts, but only on the main page of your blog. With the is_home() Conditional Tag, that task is made easy.