Speed it up:

during any given day, you can run out of things to do or buy. Therefore, here is a solution: Save your current game, and then turn the GC off. Open the lid and turn the GC on so the main GC menu comes up. Go into the calendar and change the date and/or time to whatever you want. Then close the lid and start the game. It will now be that time/day in the game and you have new stuff to buy and things to do. This works great with Halloween and "Toy Day" (Christmas). You can then switch back to the regular day and time without fault.

Easier speed up:

When you go to load your game, when asked if you are ready, choose 'before I go.' You will then get another options list. One of the options is to change the time/date - you just change it from there, and you do not have to mess with the GC's internal clock.

Money trees:

Find a spot in the ground that is glowing and dig it up. You will get 1000 bells but instead of keeping it, bury again in the same hole and a money tree will grow.

Bees into money:

It's tricky and you have to time it right, but when you knock a beehive out of a tree get your net out and catch the bees. This is the most profitable out of all the insects in the game, worth 4500.

Fossil Fuel:

After you have dug up a fossil, sent it to the museum and received it back, you can take the fossils to Tom Nook and sell them for very high prices.

Be color coded:

Place orange colored furniture in the North, yellow in the West, red in the East, and green in the South. This will give you certain bonuses. For example, the yellow furniture increases the amount of money you receive. The other colors have similar benefits, so be sure to follow this basic rule when constructing your house.

Rare Fish:

To get the most expensive fish in the game, make sure you go fishing when it rains. If you fish the shoreline when it is raining, you might catch the LIVING FOSSIL worth 15,000 bells! This also works better at night, but still only when it is raining. The shadow of the fish will be considerably larger than the others.

Golden Net:

Catch all 40 species of bugs to receive a golden net and a cool emblem on top of your house.

Golden Fishing Rod:

Catch all 40 species of fish to be rewarded with the golden rod. You will also get a cool emblem on top of your house.

Golden Axe:

Frequently visit the wishing fountain. You must fix all tasks it asks of you ranging from cleaning up the garbage to making areas more green. Get a consistently good ranking on your town from the wishing well for 15 days and you will be rewarded with the golden axe.

Golden Shovel:

See the shiny spots on the ground where you dig up your 1000 bells? Do not fill in the holes yet. Instead, you need to purchase another shovel and bury the shovel in the ground where you got the money. This will sprout a tree that will grow a golden shovel.

Golden Statue of Yourself:

If you pay off all the loans of all parts of your house, the 2 size upgrades, the basement and the upstairs, talk to Tom Nook. He will offer to erect a statue in honor of your paying off all your debt. This will be erected in front of the train station.

How to get Music:

Every Saturday night, K.K. comes to the train station at 8 o'clock. To get music from him, just say that you do not have a request. He will then tell you the name of the song he is going to play for you. After he is finished, he gives you the recording of the song he played to play in your house.

A Gift from Tom:

Give Tom Nook this code to get a rather nice gift -
4UF6T948GZ3zw3dw#%jtLEqj5ZBf
You'll receive a piece of furniture called the "starman." If you have played the old NES Mario games, you will recognize it. Press A in front of it in your home to turn on the star power.

Rock money:

First, you will need to get a shovel at Nook's for 500 bells. Then, go through town hitting every rock. Before you hit each one, dig holes around you so you do not get recoil after hitting the rock. If the rock turns red, you will get 100 bells the first 3 times you hit it. Then you will get 1,000 bells the next 3 times after that. If you can hit it a 7th time, you will get 10,000 bells!

Get rich quick with your GBA:

If you have a Game Bot Advance and the GameCube Link Cable, you can access an island to the south of Animal Crossing that lets you make money much more quickly. Collect as many pieces of fruit as you can carry, hook up your GBA, turn it on, and then go to the pier at the beach (all the way in the south). A lad named Kapp'n will be waiting here in his boat (he only shows up if your GBA is switched on) and take you to the island.

Once you're on the island, drop all the fruit you have collected and go back to the boat. Tell Kapp'n that you want to leave and that you want to transfer the island to your GBA. Your GBA will turn on and you will see your island, complete with all the fruit you have dropped. Move your hand to the door of your island animal's house and knock. Your animal will come out. Now grab a piece of fruit and put it right in front of your animal. It will eat the fruit and turn happy. After a few pieces of fruit your animal will drop a money bag of random size for each fruit you feed to your little virtual pet. Repeat this process until all pieces of fruit are gone (you can also direct your pet to shake trees to get more fruit), then put your GBA to sleep. Do NOT switch it off.

Go back to the GameCube game. Once back in your town, leave the screen with the boat and come back. Talk to the Kapp'n again and the GCN game will be updated with the new data from the GBA Island. Travel back to the island and collect all the moneybags. Some bags contain as much as 30,000 coins! You should be able to pay off your house in no time now.