Whoa... all this time, I've been spelling "cemetery" wrong, too.
I'm usually pretty good at remembering words' correct spellings after my errors are pointed out, but here are some words that have held me up in the past:
Dependent (dependant)
Weird (wierd)
Judgment (judgement)
Curiosity (curousity)
Eighth (eigth)
Accommodate (acommodate)
Anemone (anenome)
Restaurant (restaraunt)
Separate (seperate)
Threshold (threshhold)
...And not really a spelling issue, but the differences in spelling and pronunciation between "homogenous" and "homogeneous" really throw me for a loop.
If I can think of any more, I'll add them.