i would also suggest copyscape also check out > http://www.plagiarism.com/ > http://plagiarism.phys.virginia.edu/
For SE duplicate copy checking processes, you can opt for ArticleChecker.Com - but keep in mind that even re-written materials qualify as original for this free online checker. Of course, Copyscape.Com dumps major re-written materials as plagiarized to some extent. As for real originality, I'd consider hiring an editor to check your content with published online materials via Copyscape.Com and ArticleChecker.Com plus check your sources for "real" plagiarism since I believe only human eyes could determine if a write-up is plagiarized from a previously published one or otherwise. Hope this helps.
For me, I have found that articlechecker.com doesn't work as well as others that do the same thing, like Copyscape. You can place an article in both Copyscape and ArticleChecker.com that has about 75% of it's words copied from another source and ArticleChecker sometimes will not catch it. That's what I've found anyway...
run googlechecks, just copy and paste random sentences (not quotes though, as these may be widespread) from a particular article into google and see what comes up. Works well for me and my company.
that's what I used to do with my students work when i had to mark assignments. it's amazing how many unreferenced quotes you would find... even entire articles reproduced word for word!
One more facility I would suggest. http://www.dupecop.com/dupecop-desktop.php Try this. It seems to be really beneficial. I would also be happy to see some reviews on this.