DELIVERY NEWSPAPERS!
Thats what I did like a year ago...got $100/month, not bad.
The only problem is, its DEAD HARD. I mean, you have to INSERT and CREATE the newspapers, not just deliver them. Just think of one. First, you have the overall newspaper. Then, you have like 20 different flyers which you have to stuff into the newspaper, and then you have to use a rubber band and makesure it all sticks together. Now think of doing that like 100 times (you have to do 1 per house). 3 times a week.
And plus, you'll get BACK PROBLEMS and you'll start SLOUCHING. Not the best job for a young teen, but still decent money

.
Other than that, go on eBay and start merchanting. Or buy a guide that tells you how to make a living off eBay/internet.