This is not an exhaustive list but I MUST have these plugins:

Vipers Video QuickTags

Tired of copying and pasting the embed HTML from sites like YouTube? Then this plugin is for you.

Just simply click one of the new buttons that this plugin adds to the write screen (rich editor included) and then paste the URL that the video is located at into the prompt box — easy as that. You can fully configure how the videos are displayed (width, height, colors, alignment on the page) and much more. Your site will even stay (X)HTML valid unlike with the code provided by most video sites.

http://wordpress.org/extend/plugins/vipers-video-quicktags/

Share This

The ShareThis WordPress plugin provides a quick, simple to use, and unobtrusive way for users to add your post to many social bookmarking sites, or to send your post link via email, AIM, Facebook, MySpace and more.

http://wordpress.org/extend/plugins/share-this/

Dean’s FCKEditor For WordPress

This plugin Replaces the default WordPress editor with FCKeditor.

FCKeditor is an open source WYSIWYG text editor ,brings to the web much of the power of desktop editors like MS Word.it’s lightweight and is compatible with most internet browsers which include: IE 5.5+ (Windows), Firefox 1.0+, Mozilla 1.3+ and Netscape 7+.

Features:

  • media buttons
  • Build-in File manager and upload manager.
  • Build-in WordPress "read more" Button
  • Integrated with WordPress media buttons
  • Manage and insert smileys into your post
  • And MUCH more

http://wordpress.org/extend/plugins/fckeditor-for-wordpress-plugin/

WP-DB-Backup

You must be responsible for your data.  This plugin backs up your database.  Set it to a schedule of your choice and select from several locations to store the backup.

http://www.ilfilosofo.com/blog/wp-db-backup/

HeadSpace

HeadSpace2 is an all-in-one meta-data manager that allows you to fine-tune the SEO potential of your site. Visit the HeadSpace page for a video demonstration.

You can configure meta-data for:

  • Posts
  • Pages
  • Categories
  • Home page
  • Author pages
  • Search pages
  • 404 page

You can define:

  • Tags/keywords, with suggested keywords
  • Descriptions
  • Page titles
  • Custom ‘more text’
  • Site name and site description
  • Custom themes – change your theme on each page!
  • Custom plugins – load a plugin only on specific pages
  • Additional CSS and JavaScript files
  • Noindex and nofollow

It also allows you to add:

  • Google Analytics
  • Google Webmaster
  • Google section targeting
  • Mint statistic
  • 103bees
  • Statcounter
  • CrazyEgg heat map
  • Feedburner Stats Pro
  • Apture
  • Yahoo! Site Explorer
  • Microsoft Live Verification
  • HitTail
  • Piwik tracking
  • AWStats tracking

http://www.wordpress.org/extend/plugins/headspace2/

TwitterTools

For everyone on Twitter, and if you aren’t, why aren’t you, this plugin is so versatile.  It allows you to create tweets from your posts and create a sidebar widget containing your recent tweets.

http://www.wordpress.org/extend/plugins/twitter-tools/

Cathy Perkins, The WordPress Wizard