Recently some people have shared some cool extensions for Photoshop that I never realized existed. The first is Kuler and built into CS6 (and I think CS5). Go to Windows / Extensions / Kuler
Once opened, it'll appear on the panels to the right. Useful for deciding color themes for concepts or texturing! Why I never knew this was in Photoshop is beyond me. Maybe I'm the last to learn about it :P
The other cool extension is Coolorus (brought to my attention by Maury Mountain). It's free while it's in beta and provides similar functionality as Kuler, though as a color picker. http://www.coolorus.com/
So I'm also wondering what other wondrous extensions am I missing out on? Are there any that you can't live without?
[Edit] I forgot to mention MagicPicker and MixColors. I haven't used these yet, but check them out HERE