Online you won't find any really good tools, but outsourcing that assignment to someone qualified to check your spelling and grammar is one way to go.
I do such proofreading, and usually that type of work ranges from 35-40$ depending upon the length of hubpages - and whether I am allowed to do the edits directly or the text you want proofread is sent to my e-mail adress.
Editing the text in an e-mail sent to myself is much easier than having to describe in words such as "box number 3, second sentence" etc.
Hopes this helps clarify your question. :-)