How can a 13 yr. old earn cash?

I want to get around $100. I've started saving and i have $16, right now. I need to no how i can earn some cash around the house? Usually my parents give me a few dollars every so often but i need some money on a consistent basis. Maybe putting out a ad for anyone wanting their grass cut?
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you could babysit
hold a garage sale for all the useless things in your room
place a bet with friends or enemies
gamble in things your good at (eg-chess,poker,basketball...anything!)
take those paid surveys online (the most easiest)
get a part time job somewhere
do chores for money in return
have a lemonade stand or something like that.
the links given by the other answers are also a good place to check out.
Good Luck.. :)