Android Asset Studio

One of the most handy on-line icon generators I have used for android resources that will scale your resources to xhdpi, hdpi and mdpi

You can chose light or dark Holo themes theres clip art to chose from or you can scale your own images

http://android-ui-utils.googlecode.com/hg/asset-studio/dist/index.html

Also you can get a great selection of Android icons from: http://www.androidicons.com/