Screenshots? There are lots of options
But there is one I just keep coming back to for ease of use and for the right-at-hand features it provides. Intuitive editing tools make it quick and easy to use.
Skitch - In their words “Snap, Draw, Share! Skitch.com is a webservice that works hand in hand with our application Skitch to give you 1-click uploading of images for fast and fun image sharing.”
I use it as a great screen capture tool. The edit tools are perfect for commenting, making edits to a map to provide specific info that you can quickly drop into an email as well as myriad other uses. Check it out and see how quickly it will become a staple in your daily app use.
There is an intro video that will give you a great idea of what Skitch can do - http://www.skitch.com/#demo