Fishing takes alot of practice to master but once you are a fisherman the bells never stop coming in. If you want to pay off your house quickly then this is the way to do it. To view a list of fish and their prices, see Fish (GCN).
These creatures can be found in certain areas of the game and at certain times of the day and of the year. They can be sold for a certain amount of Bells, or they can be donated to the local museum. What a museum wants with creatures which were already discovered millennial ago is a matter of uncertainty, but it can be beneficial to all parties. Except for the little creature in question, perhaps. For a complete list of bugs and their prices, see Bugs (GCN).
Animal Crossing you can collect and assemble your own dinosaurs, and ancient fossils. All you have to do is go around your town and look for an X in the ground. After you dig on the X if you find a fossil you send it into the out side museum and they will turn it into bones for you. You can then either send in the bones to your town museum or sell the bones for a great price. The decision is yours. If you need a list of fossils and their prices, see Fossils (GCN).