I've been thinking about editing a lot recently (in order to make myself feel less guilty for not actually doing any editing) and have found a website called http://www.autocrit.com/ . While I wouldn't recommend anyone solely uses a website to do all of their editing (you really need to do it yourself using a book like "Self-Editing for Fiction Writers, Second Edition: How to Edit Yourself Into Print" as a guide) the website does have some useful functions for checking things that might escape your notice when you've edited your novel for the 105th time - things like overused words, repeated phrases, cliches etc.
Unfortunately it's not a free site but there is a free trial that checks up to 800 words of your text for:
- overused words
- repeated phrases
- sentence length variation
I just tested it out on the first 800 words of my novel and the results were quite interesting (I noticed a short phrase repeated in the first paragraph but, on a positive note, my sentence length did vary).
For your free trial go here: http://www.autocrit.com/CritNow.cfm
One more thing - there's also a brief, free pdf on the 3 stage of editing (which, to summarise, are: story, scene, sentence).
You can find there here: http://www.autocrit.com/pdfFiles/ThreeStepstoEditingYourNovel.pdf
Okay - really must start editing now. Stage 1 - read the whole thing all the way through.