I'm quite pleased by an effort I put into the article Scarlett Johansson recently on Wikipedia. It had been designated a good article back in 2006, but it had fallen far short of that criteria in the last couple years. It took about 3 weeks of concerted effort, but I pulled it back up and it was reassessed as a current good article.
Some of you might recognize this person as well. It's been expanded by about 80% recently, though I had quite a bit of help in getting the correct content...