I love this great little app from smileonmymac.com. It's a real time saver. They've even made pre-programed snippet files available for free. TextExpander can automatically correct misspellings and typos as you type. The free file contains approximately 100 common mistakes. The incorrect versions are added to the TextExpander snippet library as abbreviations that are replaced by the correct versions when typed.
Watch the video to see how it works. At $29.95, it's not cheap but how much is your time worth?