From Nookipedia, the Animal Crossing wiki
players to save their items in storage without having to place them into their house or pockets. The functionality of storage spaces differs between games. Clothes, accessories, furniture, flowers, Bells, stationery, tools, fruit, and many other items can be placed in storage. The only items that cannot be stored are bugs, fish, and turnips, except in New Leaf in which these can be stored, although snowflakes cannot.
In Doubutsu no Mori an individual storage unit can save a single item, but there is no limit to the number of units that can be placed in a house. In Doubutsu no Mori+, Animal Crossing and Doubutsu no Mori e+, up to three items can be stored in each storage space. In Wild World a common storage space is introduced which is shared between every storage unit in the house. Each player has their own individual storage space, and can save up to 90 items. In City Folk, this is increased to 160 spaces and a player's storage can also be accessed in the Auction House by selecting the "Checkroom" option. In New Leaf, the storage space is increased again to 180 spaces. In addition, the Train Station and Museum contain lockers that can access the storage space, even when a player is visiting another town. The lockers are available from the very beginning of the game, and so it is not actually necessary to have a storage unit at home.
Themed storage units:
Rare storage units: