Getting easy money:
• Set the gamecube clock to the New Year's Day and you will receive 10.000 bells from your parents! Try to set the clock to another year and receive more bells!
• Walk beside a rock and dig around your character, thus, you can get more money from the rock because your character won’t bounce from the rock.
• Take some fruits which are not native to your city, plant them and let the tree grow. Then you can sell your fruits to Nook!
• You also can grow a money tree, if you plant a money bag into the ground. Find a glowing spot on the ground, unearth the money bag with your shovel. Now go to your inventory, select the money bag, then choose the "plant item in ground" option and put the bag back into the spot.
• Note that every day one rock turns to a treasure one! You should hit it with the shovel, hit it about seven times and get one money bag per one hit (you can get it only when the rock is red!).