Google Developers Group
In our company, we focus on 4 screen configurations:
This covers "most of the needs" and almost corresponds to number of sizes iOS has. I am interested how other developers deal with the issue, especially for new phones like Samsung 5 inch Note that seems to be in the no-man's land.
Here is an interesting, but not very informative article.
There are more versions to design graphics to if you want to support as many Android devices as possible: Notification icons changed with version 2.3 and again with 3.0, menu items icons changed with version 3.0 and menus are being phased out in favor of dialog fragments starting with version 3.0 (with yet another icon format replacing the menu icon). API classes and methods are being deprecated or phased out without an adequate replacement, and features are not orthogonal (handled differently in different classes).