Back in 2008 - 2009 I wrote for The Next Web for fun. As a blogger, timing from breaking news to hitting the publish button was critical. This meant grammatical errors were often casualties of the rush to publish.
It was during this time I started using Mac's built in Text to Speech technology to assist in proofreading. I'm an auditory person so hearing what I wrote helped quickly identify errors.
To active text to speech go to System Preferences > Dictation & Speech (and select the Text to Speech tab). There you can set the hotkey, voice and the speech rate. Once activated simply highlight your post or whatever text you want to proofread and type the hotkey. Boom!