Some good sources for identifying rocks are geology.com, About.com and National Geographic. A good source teaches the reader the differences between categories of igneous rocks, sedimentary rocks and metamorphic rocks.
The sources also teach the reader how to identify rocks through such characteristics as grain size, foliation, color, hardness and taste. A good source then focuses on individual rocks in one of the three categories. For example, an igneous rock of any color that is very coarse, with small, intrusive bodies and a granitic composition is most likely pegmatite. A metamorphic rock that is foliated, with a fine grain, light color and a soft greasy feel is most likely soapstone.