Great source of both free and commercial themes as well as WordPress tips and tricks.
Tag › tips
WPMU.org is the best daily source of WordPress, Multisite and BuddyPress news, plugins, themes, tips and support.
WordPress Tavern is a site focused on all things WordPress. On top of that, we also cover BuddyPress, bbPress, any project under the Automattic umbrella etc. WordPress Tavern is a warm and inviting community where those interested in the software can hang out with fellow WordPressers to engage in enlightening discussions. On WPTavern, you’ll find reviews, news, screencasts, guest blog posts from some great community members and much more.
WordPress Hacks was launched nearly three years ago for reviewing WordPress themes, plugins, as well as providing tips and resources to the community.
It is one of the best places to start learning how to hack WordPress, I know first hand cause I visited it a lot when I started coding for WP.
Lots of great tips and general hacks that you can use to make your site more powerful.