DroidAssets allows you to generate all the assets you need for your Android application in record time. Drag-and-drop an asset from the res/drawable-{density} folder, and this asset will be generated for all the other densities you need. This works not only for simple PNG's, but also 9-patches.
- Resize PNG assets
- Regenerate 9-patches for reduced images
- Place the generated images in the right drawable folder