An obvious solution is to use MS Word, if you have it, and turn on the option to 'check grammar as you type. Or maybe: http://www.gingersoftware.com/grammarcheck/

This is a very good program for improving English writing http://www.polishmywriting.com/

That will probably solve about 60% of your problem. ;) Still, the above suggestions are OK.

www.engvid.com