Free

Make Money

Make an Extra $8.70 on Each of Your WordPress Themes
LifeGuard Assistant Plugin – Make Money from WordPress Themes

Increase Conversion

Re-Evaluate Popular (and Unpopular) Pages and Posts to Increase Conversion
Keep Visitors from Leaving with WordPress Popular Posts
Keep Visitors from Leaving with WordPress’ Yet Another Related Posts Plugin
Offer Downloads

Social Media

Adding Google Authorship to WordPress Posts

Search Engine Optimization

The Canonical Tag Explained and How WordPress Handles It
SEO Friendly Dynamic <title> for WordPress

WordPress Themes

Excellent Places to Get Quality WordPress Themes
Theme Review: Tweet Archive Theme

WordPress Plugins

WPMU – Quality WordPress Plugins
Put the Google+ Add to Circles Badge with a WordPress Widget

WordPress Contact Forms

WordPress Security

7 Code Snippets to Improve WordPress Security
The Correct Way to Remove the WordPress Version to Increase Security
3 Excellent WordPress Security Plugins

Speed up WordPress

Speed Up your WordPress Site with W3 Total Cache
Figure Out Which WordPress Plugins are Slowing Down Your Site

Web Design