Its three. Crows can count that much.
Let's see there's ... Amazon, Barnes and Noble, Android Marketplace, GetJar, various device manufacturers (Lenovo, Motorola, General Mobile), and various phone companies around the world. http://royal.pingdom.com/2010/12/30/the-ongoing-mess-of-andr...
There's probably at least a dozen, if not more.
This sounds like a case of "damned if you do, damned if you don't".
If all the app stores were just stores competing on a level playing field it would be a good thing, but they're obviously not. Most of these are not real "stores", they are schemes for extorting money from users and developers by removing (not enhancing) their ability to choose.