I had never seen this website until Roger Ebert posted a link to it. He is probably the most prolific twitterer on the interwebs so I usually click on the links he posts. While grammar is never a very sexy topic I think it is important. I am not the most perfect picture of grammar, but I am way above average. This post from the Oatmeal details several words that are often confused and misspelled. Check it out.
I see people misspell these often.