LEGO can be used to make a wide variety of furniture, most typically at minifig scale, which help make a building appear more realistic and "lived in." Examples include chairs, tables, kitchen appliances, beds, hot tubs, and even bathroom fixtures.
Sample Furniture Ideas
A small rectangular desk is easily made from a brown 2x4 plate, supported by 1x2 bricks, as illustrated in this example, which also shows a pull-out keyboard tray (made with a 2x2 plate stuck to the underside of the desk), and a 1x1 yellow tile as a pad of notepaper.
This corner desk on BrickShelf (at right) also demonstrates a nice desk lamp and a laptop computer.
Chairs are useful in a lot of different rooms. LEGO supplies a Minifig Chair part but for variety people have built lots of different ones. A particularly well rounded collection of chairs can be found in the gallery of Michael Jasper, linked at left.
Beds are fairly simple: usually just a plate, sometimes covered with colored plates or tiles for a comforter, and raised plates for pillows. However, there are many creative variations.
Good legs for beds and other furniture can be made with a 1x1 cone on top of a 1x1 plate, as shown here.
This folder on BrickShelf demonstrates a fully stocked kitchen, complete with cabinets and a variety of appliances.
If your minifigs are serious coffee drinkers, consider giving them a quad espresso machine.
A toilet is typically made with a 2x2 round tile on top of an inverted 2x2 slope, in front of a 1x2 brick with a tile on top. A roll of toilet paper next to it can be made with a pair of 1x1 round plates joined to a Part:4081. Both techniques are shown nicely in this BrickShelf image.