There are many situations where you want to make sure that certain categories only appear on some pages, and not on others. Here are a few WordPress plugins that can help you do this without having to hack your template files:

Front Page Excluded Categories WordPress plugin – this plugin enables you to exclude posts from certain categories from your front page. This is possible by hard coding your template files as well, but for those who want to give others the ability to do this easily, or who just don’t want to mess with their template files, this is a good solution.

Advanced Category Excluder WordPress plugin – this plugin gives you more flexibility over where categories appear. Here, you have access to modifying categories for five different pages on your blog: archive, home, rss posts, rss comments and search. It currently does not work for tag pages.