How many types of apples are there?

More than 7500 known cultivars with ranging characteristics.

Elaborate:

So an apple is basically an apple and minor differences have been cultivated to suit different purposes: eating, cooking, ciders, etc…. Below are the top 15 varieties that account for almost 90% of 2008 production (according to the U.S. Apple Association):

The site also has this nice ‘Apple Variety Guide‘ which highlights common aspects and differences between the top varietals.
Keep in mind this is less than a percent of all apple cultivars in the world so expect to see different types when you go to your local grocery store as many are probably too obscure to leave their immediate region.

How Many Types Of Apples Are There
[reasonI thought that there were different sub-species of apples. Also, since many probably don’t leave their region, it’s interesting to see the range in characteristics required and desired depending on the region, climate, etc….[/reason] Source: Wiki: Apple
Source: Wiki: Apple Cultivars
Source: US Apple Association: Apple Varieties
Source: NY Apple Country: Apple Cultivars