According to BusinessWriting.com, these are the 25 most commonly misspelled words in English.
I don’t consider myself a very good speller, for an editor (I just look everything up). But this test seemed easy to me. The only question that I thought was a little tricky was the one that asked about a British spelling, since I’m only familiar with U.S. style. I figured it was a trick question and answered with the U.S. spelling, which luckily was right.