Don't feel bad...everyone does it. For fun, below the list are some URLs that have quizzes and other word lists.
absence
absurd
accidentally
accommodate
across
advertisement
all right
a lot
amateur
athletics
attendance
beginning
believe
business
coming
committee
condemn
conscious
convenient
correspondence
criticize
definite
dependent
descend
description
desperate
develop
difference
disappoint
dispensable
embarrass
environment
equipped
escape
exaggerate
excellent
existence
experience
familiar
fascinate
foreign
forty
government
grammar
guidance
humorous
imaginary
immediately
independent
irresistible
laboratory
lightning
losing
lovely
misspelled
necessary
neighbor
niece
occasion
occurred
occurrence
omitted
opportunity
parallel
parliament
performance
permanent
pleasant
possess
prejudice
privilege
professor
receive
recommend
repetition
restaurant
rhythm
schedule
separate
similar
success
surprise
tragedy
truly
villain
weird
writing
Other Commonly Misspelled Words- http://www.wsu.edu/~brians/errors/misspelled.html"
A Spelling Test (done by an actual publishing editor)- http://www.sentex.net/~mmcadams/spelling.html