Ways to make money without Time traveling or Wifi Connection
When ever you receive a fruit that is not native to your town bury it to make a fruit tree. These fruits can be sold for three times as much as any fruit native to your town. Once the tree has grown shake it and plant all of the fruits that drop and repeat this process until you have 30-50 fruit trees. Empty your inventory and slowly sell all of the fruits from the tree. The trees will regrow their fruit every 2-3 days so this strategy is effective but slow.
Fishing and Bug catching will also bring in a few bells and is a good way to make money if you know where the rare fish and bugs are. This strategy is also the most fun and doesn't seem much like work.
Creating hybrids of flowers can also earn you up to 8,000 bells per flower so if you can create a huge garden you can quickly rake in the cash.
Collecting the fossils burried underground can earn you 5,000-8,000 bells per fossil.
Ways of making money with Time traveling and Wifi Connection
Set your clock to differnt events during the year so that you can get the exclusive items. Since many players do not like to TIme Travel they will have no way of getting the items. You can then resell the items for 100,000 bells and up.
Being nice to your neighbors can earn you a good reputation. If you are really nice to your neighbors you will receive photographs of them. The items are highly collectable and hard to get. The market on the pictures go from 100,000 bells up to 1,000,000 bells a piece!
Create 4 character in your town even if you don't need them. When special characters visit your town such as Sahara and Pascal get the items that they give you 4 times, once with each character. There is a huge demand of these exclusive items since nobody knows when they will visit your town. Resell the four items for high prices to easily earn a few bells.
One easy way to make money is search peoples' towns for rare items they do not need anymore. Try and get them for free or at a low cost and then find other people in search of the item and sell it to them for a higher price.
HINT:When you get money put it in the bank right away because it will then earn intersts giving you extra cash for doing nothing!
If you follow all or a few of these strategies you will easily be able to buy the largest house possible and and still have a few million dollars left to spend as you please. The best part is once you are done you will never have to work again!