Map 1: Dot Density
A dot density map uses dots as a way to show the concentration in a particular area as shown by a data set. For example, if a dot is 1 million people, major cities in the United States would have a dense number of dots on them compared to rural areas, which would have very few. Dot density maps are useful for showing the number of things, events, or occurances over a large area.
Map 2: Chloropleth
A chloropleth map is one that uses distinct areas, and shading of those areas, in order to convey information about those areas. Political maps used to show the swaying of states toward Democrats and Republicans are often chloropleth maps. The colors used in the map usually convey a density of concentration--an election map that is deep red is associated with a Republican state is contrasted against a light red state that is not as strongly associated with the party.
Map 3: Isarithmic
It's a kind of map that shows the areas where things occur. For example, one would use an isarithmic map in order to show weather patterns in an area. The cordoned off pieces of the map are called chorograms. They show distinct pieces of data that separate sections of map, comprised of data sets, off from other, different sections.
For example, I have created the isarithmic map of rain fall patterns in GA below.