The *irregardless* mistake mentioned before.( My boss says that!!) ;)
The *loose* for *lose* mentioned before.
Personally, i'm a decent speller for long words.
But sometimes i get the easiest everyday words wrong.
*Definite*, mentioned before, I know I get wrong sometimes.
*Probably*, I spelled wrong for awhile.
I think b/c you get used to doing it wrong, and no one calls you on it, then when it's brought to your attention, you feel like an ass for having done it wrong so much. :p
I remember having problems with *with* and *which*in grade school, but actually did pretty well in spelling bees. Go figure!
Mostly i try not to let the mistakes bother me too much, because so many times it's either a kid or someone with a bit of a learning disorder, so....