- WP Seek – look up anything WordPress on wpseek.com.
- WP Function Reference – look up a function in the reference on the official WordPress codex.
- WP Action Reference – look up an action hook in the WordPress codex.
- WP Filter Reference – look up a filter hook in the WordPress codex.
It’s not hard to roll these, and you can make some yourself. Here’s an example. Just make a few changes and strip out the white space.