Grammarly is so much more than a spell checker! It will also help you with your grammar.
I am one of those people who has awful handwriting and I use this when I can't spell a word (making it eligible so no one knows!). I also hate sending emails to one of my good friends and colleagues (hello Michelle), because I know all my commas are in the wrong places. I have only been using Grammarly for a couple of days and it is already not only making me feel more confident about my written work, but it is helping me learn a lot too!
Grammarly is free. I've added it as a Chrome Extension and I've downloaded it to my desktop, (though I really only ever work in my browser). It will highlight mistakes and give you suggestions to correct it, and I have used it mostly with my email. At the moment it does not work with Google Docs, but you can upload documents to the website and have it check them there too.
Although I couldn't screen shot the suggestions it was given me, I can show it highlighting some problems in my non-sensical email:
Oh and their Twitter posts pretty fun things too: