1) In the street or sidewalks, sometimes whenever I go out, I happen to find a quarter or a few pennies lying about, so to me that's just free money right there.
2) Under the couch, seems like a cliche reason, but usually a lot of loose change is there, I sometimes find loonies or quarters mostly, another earning of free money right there.
3) Piggy banks, usually some people have them, and they are not that smart when it comes to not hiding it properly, so whenever they are away, you can just go to their piggy bank and take all their change, no one will ever be the wiser.
4) Pants, yes, pants. By checking pants in your room. You'll happen to find some loose change right there at the spot, checking other peoples pants can improve for finding more change, risky, but the reward is good.