I've been looking around for a good set of Android map marker icons (drawables), and I've only seen a few that included a vector image (Illustrator or EPS graphics) so I could customize the icon however I wanted. So, I just created my own icon, saved five common colors to a set of xhdpi, hdpi, mdpi, and ldpi sizes, and posted them to a new repository on GitHub: Android Map Marker Drawables (icons).
Please see the GitHub repo for more information about the icons, how to use them, and for the original vector image. Here are examples of the icons (in hdpi resolution):
Here's an example app screenshot using a MapView with these icons as the map's Drawable: