1. WordPress Database Backup – The WP DB Backup plugin by Austin Matzko lets you run complete backups of your WordPress database including plugin tables and other external content. You can even choose what tables you want to backup and what tables to ignore. There are multiple ways of receiving the backup, by email, saved to your computer, or saved to your server. I like Morten’s suggestion of using a dedicated gmail addy to have the backups sent to. I have been using this plugin for quite some time and find it convenient and easy to use.
   

   WP Database Plugin

2. Akismet – vital comment spam moderation – This plugin comes installed with the installation of WordPress.  You will need to activate the plugin before it will work and it does require an API which is Free.
3. All In One SEO Pack – Pump up your site findability – The key to SEO (or Search Engine Optimization) is to give your site, pages and posts a descriptive title, a short description and the right keywords. The All in One SEO Pack plugin adds a new field to your post and page edit areas inside WordPress where you can set separate title, description and keyword attributes for your articles.
4. WPTouch – one-click mobile theme for your site.  WPtouch automatically transforms your WordPress blog into an iPhone application-style theme, complete with ajax loading articles and effects, when viewed from an iPhone, iPod touch, Android, Opera Mini, Palm Pre, Samsung touch and BlackBerry Storm/Torch mobile devices. I have not tried this plugin as yet but will test it out on my experimental bog to see how it works.
5. WP Typography – proper typography for the web. Improve your web typography with: hyphenation, space control, intelligent character replacement, and CSS hooks.
6. WordPress.com Stats – local stats for your site. The WordPress.com Stats plugin brings the same kinds of visitor stats you’d get on a WordPress.com site to your self-hosted WordPress site. For the plugin to work you need to have a WordPress.com API (which requires a free account) and you can run stats for multiple sites under that one API. I installed this plugin early on for my WordPress blogs.
7. Contact forms: Two options for two scenarios. Morten recommends Clean-Contact if you only need one contact form and Contact Form 7 if you need to use more than one form. I have not tried either of these plugins as I am happy witht he contact form I am currently using.
8. Fancybox for WordPress – Showcase your photos in style. FancyBox gives you the option of adding a lighbox display to your images. I have not tried this plugin as yet but will give it a test run on my test blog first.
9. ShareDaddy – interactive social network sharing buttons. Share your posts with Twitter, Facebook, and a host of other services. You can configure services to appear as icons, text, or both.
10. WP PageNavi – paginated navigation for all. Adds a more advanced paging navigation to your WordPress site.

Read 10 WordPress plugins I use all the time by Morten Rand-Hendriksen.

You might also be interested in WordPress 3.0 Essential Training with:  Morten Rand-Hendriksen available from Lynda.com.