Debi -- who do you bank with? I've had pretty good luck getting those charges reduced or altogether eliminated. I'm with B of A, and they'll usually write off your first mistake. Or they'll eliminate it if you promise to link your savings account to your checking account... so that if you overdraw your checking account, it takes money from your savings account. It's worth a try anyway. They charge WAY too much for overdrawing an account by a few dollars, and they know it, so they're a bit flexible.
I had the same thing happen, and I got really mad at my fiancee (we share an account). The problem was, neither of us was in charge of the account, so no one was watching closely enough. Also my fiancee is a NUT about putting away a little money to our savings account as soon as one of us gets paid... but that doesn't help you if you then have to pay $100 in charges because you overdrew your account does it!!!