The Ardent Epicure

This delicious fresh cheese is a common Italian ingredient used in both savory and sweet dishes.  One of the most versatile cheeses around, it has a soft and creamy, sometimes lumpy texture, and is fairly moist in comparison to many other cheeses.
While most cheeses are created from curds made by boiling milk and adding some sort of an acid or culture, ricotta is actually made from the by-product of the cheese making process, whey.  Whey is basically the liquid that is drained off from the curds when making other cheeses.  This whey is also heated, and the curds that form from the whey itself make up the basis for wonderful ricotta cheese.
Types of Ricotta
Today, you can find ricotta cheese in most any grocery or specialty foods store.  It often comes packaged in a bucket of some sort, and can be found in varying degrees of moistness.  While the ricotta you are likely to find in your local store will be made from cow's milk, in Italy, it is also common to make this cheese from sheep's milk, and it is possible to create it from other types of milk as well (i.e. goat's milk or water buffalo milk).

Cured or cooked varieties of ricotta are also in existence, but the ricotta you find in a supermarket is likely to be fresh ricotta.  This ricotta has a mild, subtle, somewhat sweet flavor that is not overpowering, making it a great cheese to use when you want to promote the flavors of another food in your dish.
Uses
Ricotta is very often used as a filling (or filling base) for stuff pastas, such as ravioli, manicotti, canneloni, tortellini, tortelloni, and lasagna, among others.  It is also often used to top pizzas, or in folded pizzas (calzone).
Ricotta is also used in sweet dessert dishes, such as cannoli (one of my favorites) and other types of desserts that use cheese.  In both situations, the cheese is often mixed with other ingredients to make a more robust filing, as the flavor of the ricotta in and of itself can be considered bland.  For instance, adding chocolate chips for a cannoli mixture, or adding mozzarella and spinach for a ravioli mixture can use ricotta as a delicious base for wonderful fillings.
Ricotta Terms
Requesón - the Mexican version of ricotta, used in some dishes such as tostadas.
Ricotta Affumicata - smoked ricotta.
Ricotta Infornata - baked ricotta
Ricotta Scanta - cured ricotta
Mini Recipe Idea
When you make pizzas at home (see Making Your Own Pizza), try taking small amounts of fresh ricotta, rolling it into balls, and placing a few on your pizza.  The ricotta will melt a little bit (and start to brown if cooked long enough), and create an amazing texture and flavor that goes well with other cheeses and toppings.
Enjoy!