Below is a list of my favorite Drupal 6 modules:

• Views : A module to create queries and display data
• Pathauto : Automatically create SEO URLs
• Admin_Menu : A MUST for all drupal developers and site administrators
• Search404 : Give your users relevant search information for all 404 pages
• TinyMCE + IMCE : WYSIWYG Editor (TinyMCE), Image upload and maniuplation (IMCE)
• Image : Easily create photo galleries