I've been saving these up 'til there were enough of them to post:
As Heather noted in a comment to an entry last August, antidote and anecdote are often used in place of each other.
Here are some other common misspellings I've been seeing lately, along with some examples of misusage (the asterisk indicates the sentence is wrong). Some of these are especially tricky because the misspelling is a real word, so spellcheckers won't catch it. One is even trickier 'cause it's not actually wrong according to the dictionary. :)
- whisp for wisp (but MW3 lists whisp as a valid variant spelling, sigh)
- whither for wither (as in * "The plant whithered away"—especially confusing because "whither away?" is archaic-speak for "Where ya headed?")
- eek for eke (* "He eeked out a living by fixing shoelaces.")
- in tact for intact (* "The old manuscript was still in tact.")
- This one's just a simple typo, but a very common one: out for our, or vice versa.