Lead and led and other common slips
I've noticed how many otherwise very good spellers get confused and write lead when they mean led as in I led the way. It has always baffled me, as I don't think I've ever got the two confused myself. It just occurred to me, however, that the probable reason is the similarity with the verb read, for which the past tense is of course read, pronounced red.
It's interesting to see the most frequent spelling errors, especially those that crop up in the written English of otherwise competent spellers. Awhile rears its head quite often. There is a word spelt awhile, of course, but it can't be used in place of every occurrence of the phrase a while. A related error, which I am quite surprised to see is so widespread, is writing alot for a lot, despite the fact no such word exists in written English according to the dictionaries. It is so common, in fact, I wonder whether it won't be long before dictionaries start to recognize it as a legitimate variant. It also seems to be an exclusively American phenomenon.