I would recommend Lightscreen or Snipping Tool usually but when it comes to doing quick and easy annotations, I have started to find myself relying more and more on Greenshot.
This little tool seems to be quite heavy on options (maybe too heavy) but it also offers some satisfying features that enable you to essentially run a one-stop-shop for snapping, editing, and annotating all in one.
I strongly encourage you to give it a spin!
http://getgreenshot.org/downloads/
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| This image snapped and edited with Greenshot |
