Awesome tips on tools, @Ryan Thanks for sharing them.
For Mac users, here are some similar tools, although I'm guessing some Mac users know of them.
I use Skitch primarily for screen capture and sharing images or linking it to an image control. I also find myself using Cloud App a lot more since they also added support for screenrecording as animated gif. But for basic screen capture it's also great. Both have some limited / free options..
OS X has a great tool called Digital Color Meter (under /Applications/Utilities) that samples a color from your screen and can copy sampled hexadecimal color value to your clipboard so you can paste it into the color picker in Mockups. There are quite a few color picker tools you can add to the Mac, and one that I've had installed on my machines for years that runs next to the visual OS X color picker is Hex Color Picker, and I still use that primarily.
For measuring elements on the screen, XScope is great, and FreeRuler while super old, still works perfectly. Useuful if you're measuring elements from a screenshot or something.
Another neat tool that I use a lot is a simple window manager called Divvy ($14) that comes in Mac or Windows version. Hit a keyboard shortcut and you can precisely position a Mockups window in one area of your screen, and another application window in another screen, or whatever.
I use Illustrator for various different stuff (print work, and other tasks that utilize old scripts and batch actions built up over the years). For production work, Sketch App has been the primary design tool for everything else.
Would love to see other peoples' tips on other tools they use. Thanks for starting this thread, Ryan!