1. Insights - Googling inside your admin panel when writing new post.
2. NM Delete Revision - Useful plugin to decrease export file size when you planned to migrate all your posts, comments, etc.
3. DB Cache - The fastest cache engine for WordPress, that produces cache of database queries with easy configuration. Better than WP Cache or WP Super Cache.
4. WP Note - Cool wordpress plugin to catch readers attention on your posts.
5. WP Twitip ID - adds a field to the comment form for a user to add their twitter username.
Okay, it's enough for now.
You can have simple, concise stats with no additional load on your server by plugging into WordPress.com's stat system.
WP super cache
A very fast caching engine for WordPress that produces static html files.
IntenseDebate comments enhance and encourage conversation on your blog. Build your reader community, increase your comments, & boost pageviews.
Get Recent Comments
Download Display the most recent comments or trackbacks with your own formatting in the sidebar.
Related Ways to Take Action
Download The “Related Ways to Take Action” WordPress Plugin makes it super easy to connect your readers to ways to take action based on the content of your
those are some plug-ins in WP ...
I dunno there's so much plugin that WP has. I just know cloud tag and standard widget that already there on WP ha ha ha