Yummy Honey
Plant flowers on your farm and then bees will come and build hives in your apple tree. Honey can be collected everyday (even in Winter!). It is worth 50G, but if you give some honey to Louis, the price will go up to 60G. :)

Easy Money
Note: This trick requires two memory cards and a file which has some type of animal (preferably cows or sheep). Copy the file to memory card two, then play the game on either file. Go to your diary and choose to exchange animals. Have an animal come in from the other memory card. When this is done, sell the animal repeat as many times as needed.