Are there any online/standalone editors or template collections for designing Android application?
It would be difficult to find a site with templates for android apps, as each app has different functions. You don't specify what platform you are using for developing them, so I'm assuming you will use HTML. In that case, any template for 320px width or responsive template that includes mobile will work.
If you are creating your app from zero, I'd recommend you start with a UI kit for 'inspiration'. Some are: