The second layout is the U.  This is a design which can make very efficient use of a narrow space.  Because it uses three walls, there is plenty of space for your "work triangle" - but more about that later.  It does not work well for a kitchen with multiple cooks, unless your aisle is very wide.

Layout number three is the galley-style kitchen.  It is similar to the U, but it eliminates the wall on the end, leaving two parallel walls.  Although this design gives you less workspace than a U-shaped kitchen, it allows access to the kitchen from both ends, which can be very useful.

The next layout is the wall-style kitchen.  In this layout, all of your appliances are lined up along a single wall.  It is not a very efficient design for the cook, because you are constantly moving from one end of the kitchen to the other.  However, if you are very limited on kitchen space, this is very much a space-saving design.

The final layout is the double-L.  This is a good layout for larger kitchens.  It consists of a large L, running along two connecting walls, then a smaller L which has one leg against the third wall of the kitchen, with a peninsula extending into the kitchen.  The double-L is the design preferred by many gourmet cooks because it gives you lots of space for various appliances, as well as extensive countertop space.

An alternative to the work triangle approach is the zone approach.  With this method, each part of the kitchen has a designated function.  For instance, you may have a prep area, which would include the sink for washing vegetables and an integrated cutting board for chopping them.  You could also have a cooking zone, which would include the stove, oven, microwave, and cupboards within easy reach to store baking dishes; or a baking zone, which would be near the stove and include space for your cookbooks, baking sheets, and ample counter space for rolling out dough.  The zone approach works especially well if you will have multiple cooks working in your kitchen at the same time.