The first tool I can't do without is the Windows 7 Snipping Tool! I use it nearly everyday! I find just the right graph online, or need just a small section of a worksheet, or want to include just a few words from a post ... the Snipping Tool makes all of that possible! So easy!
I use CamScanner, an app on my phone, almost everyday. CamScanner will scan a document in as a pdf and from there you can share it to various media. I simply hold my phone over a document, student work, my notes, a key that needs to be posted; then take the picture, and the app does the rest. Super easy, and faster than the old scanner I have here at home!
Fireshot is a handy Chrome app. FireShot helps you capture web page screenshots, perform quick edits, add text annotations, and save the captures as a PDF or image file. It's a quick way to get a copy of a webpage needed as a reference.
Last up for now is PicMonkey! I love to use it to put text on pictures! It's simple and free!
Well I said "last" but I do want to mention that I am really enjoying ThingLink! I can see how it is going to be a great tool for student work as well as a teaching tool. If you haven't checked it out, take a look at this and this!