Flats

These are your traditional terry towelling or flannelette nappies.  They are usually just called "Terry Flats" or "Flannelette Flats".  You can also get Bamboo Flats now (very absorbent and soft) and muslin nappies which are flats.

Flats are inexpensive and versatile, and many people like these as the backbone of their nappy system.  You can buy a couple of dozen or more and use them a lot with a newborn, gradually replacing them with fitteds, pockets and other nappies as your baby gets older if you want.  That way, you don't have a huge expense at the outset.  Also, newborns grow out of fitted nappies quite quickly, so you are better to wait and get more of these when your baby is a little bigger so the nappy will fit for longer.

There are two important things with flats though.

Firstly, make sure you have a good cover.  Don't just get a pull up plastic thing from the supermarket.  Invest in a couple of good PUL, Fleece, or Wool covers. 

Secondly, learn good folds.  Here is a link to a site that has lots of good nappy folds. 

Terry Folds:  http://www.thenappylady.co.uk/Advice/Instructions.asp?InstructionID=2