Starting with the Base
I have never met anyone that didn't like one kind of pie or another. While I have known very few people who don't like the crust, I think most would agree that a pie isn't a pie without a good crust. The key to making a delicious pie is using the proper type of crust. Pie crust is not hard to make contrary to what you might believe. The most important thing to remember is to not over work the dough. Over working the dough develops gluten resulting in tough pie shell. I will discuss the common types of pie doughs today in the order I consider easiest to most difficult and finish with specialty pie shells.
The crumb crust - The crumb crust is usually made from crumbled up cookies or crackers, the graham cracker crust being the most popular. The crumb crust can also be made from any dry and/or short type of cookies. The flavor of crumb crusts can vary greatly depending on the type of crumbs used. Crumb crusts require no rolling. The crumbs are mixed with melted fat and possibly sugar to add enough sweetness and then pressed into the pie plate. Some crumb crusts are baked and others chilled before adding the filling. Because crumb crusts are usually dry and crumbly they are best suited for fillings with a sturdy body, a cream pie or cheesecake for example.
The sweet or cookie dough - The reason this dough is called cookie is because it is often made in the same fashion as making cookie dough. The dough is delicate and sweet and can be chilled and rolled out to fit in the pie plate or tart pan or pressed directly into the pan. This dough is usually fully baked before filling. The sweet shell is best suited for sweet fillings.
Mealy pie dough - Mealy pie dough is used for wet type filling that will be baked in the shell, pumpkin pie, quiche or fruit fillings. The dough must be sturdy enough to hold in the liquids until they set. Mealy pie dough is made by mixing the butter into the dry ingredients evenly and then adding enough liquid to form a dough. Care needs to be taken not to over mix the dough once the liquids are added or you will get a tough dough. Mix only until a dough can be formed.
Flakey pie dough - This is the one that scares everyone! The secret to flakey pie crust is to only mix in the fat until there are several pea size pieces remaining and when the water is added to only mix until a loose ball forms. Using ice water is important as well because it helps keep the gluten from developing and keeps the fats solid. A properly made flakey pie crust will still have visible chunks of fat in it after it is rolled out. Flakey crust is best suited for fillings of firm fruit, nut or meat fillings.
Specialty crusts - a crust can really be made from anything as long as it compliments the filling and is adequate vessel for holding the filling together. Meringue filling is great for lighter fillings like chiffons. Nuts are also widely used in crusts. Potatoes can make a great crust for savory pies. Use your imagination, the pie is the limit.