I am a plugin junkie. Here are a few that I like to install right after setting up WordPress.
Akismet
The quinessential WordPress comment spam stopper, Akismet is part of a WP base install. In addition to installing Akismet, go to Options > Discussion and decide how much control you want over comments.
By Matt Mullenweg.
Go to Plugins > Akismet Configuration to enter your free WordPress.com API Key.
Akismet checks your comments against the Akismet web service to see if they look like spam or not. You need a WordPress.com API key to use it. You can review the spam it catches under “Comments.” To show off your Akismet stats just put in your template.
Google XML Sitemaps
Never say never to Google. Make sure to enable Update Notification, especially “Modify or create robots.txt file in blog root which contains the sitemap location.”
Configuration Page By Arne Brachhold.
Configuration is at Options > XML Sitemap
This plugin will generate a sitemaps.org compatible sitemap of your WordPress blog which is supported by Ask.com, Google, MSN Search and YAHOO.
Subscribe To Comments
Very handy! I seldom appreciate signing myself up for a mailing list as much as I appreciate getting notice of an ongoing conversation in a blog. Blog comments have become an important part of online community-building. Subscribers can manage their own subscriptions. If you use this, be sure to add a line to your privacy policy or comment policy about how you use any collected email addresses.
By Mark Jaquith.
Configure at Options > Subscribe to Comments
Manage subscriptions at Manage > Subscriptions
Allows readers to receive notifications of new comments that are posted to an entry. Based on version 1 from Scriptygoddess.
Top Level Categories
I use this because I like stripping off layers, and WordPress likes to make available lots of lists or how posts might be grouped. If I wanted a table of contents for categories, I’d put it in sidebar navigation or a sitemap.
By Filipe Fortes.
No configuration needed, simply activate.
Removes the prefix from the URL for a category. For instance, if your old category link was /category/catname it will now be /catname.
Ultimate Google Analytics
Sure, you can just paste your tracking code to the footer.php file. Why not let Google Analytics do a little more?
By Wilfred van der Deijl.
Configure at Options > Ultimate GA.
Enable Google Analytics on your blog. Has options to also track external links, mailto links and links to downloads on your own site. Check http://www.oratransplant.nl/uga/#versions for version updates.
WordPress Database Backup
You need this, because accidents and disasters happen and it’s not nice to be without a backup. Database backups can be created on demand or automatically.
By Austin Matzko.
Configure at Manage > Backup
On-demand backup of your WordPress database. Navigate to Manage → Backup to get started.
All in One SEO Pack
Do you need it? Maybe, maybe not. Do you want to play with it? Come on, of course you do.
Let the plugin fill in the blanks for you, or choose specific titles, keywords and descriptions for each page and post, or do a little of each.
By uberdose.
Configure at Options > All in One SEO.
Out-of-the-box SEO for your WordPress blog.
cforms II
Cforms is fun to use. Use it to create multiple forms with distinct purposes. Includes help files, examples, and way more configuration alternatives than you’ll probably need for any one form.
By Oliver Seidel.
Configuration and more at the CformsII tab.
cforms II offers unparalleled flexibility in deploying contact forms across your blog. Features include: comprehensive SPAM protection, Ajax support, Backup & Restore, Multi-Recipients, Role Manager support, Database tracking and many more.