1. Google Doc Embedder
Google Doc Embedder lets you embed PDF files, PowerPoint presentations, and TIFF images in a web page using the Google Docs Viewer (no Flash or PDF browser plug-ins required).
2. Search Engine Optimized Plugin
This plugin will optimized your blog post /page search setting, by using this setting your pages /post will be easier to searh on the common search engine like Google, yahoo, etc.
3. Event Calendar Plugin
This is actually a plugin to show calendar, and you can also added an event to it and show it on the sidebar using widget.
4. WP-Polls Plugin
This plugin provide you a polling features for your blog, with this plugin you may ask your vistor to fill out pools that you created.
5. Add to Any: Share/Save/Bookmark Button Plugin
This pugin will Helps readers share, save, and bookmark your posts and pages using any service.
6. Author Avatars List
This pugin will show your avatr picture on your sidebar.
This Plugin enables user to upload and show your own avatar.
8. WordPress Mobile Edition
Turn your WordPress into a mobile website/blog automatically.
9. SI CAPTCHA Anti-Spam
Adds CAPTCHA anti-spam methods to WordPress on the comment form, registration form, login, or all. This prevents spam from automated bots.