While most of our efforts revolve around advanced features in the Eclipse plug-ins, you can develop Android applications using many other tools -- Maven, IntelliJ, NetBeans, etc. Soon there will be a link on the main developer site with more information on this.
The Android Developer Tools project is deliberately trying to support other IDEs and tools. We have extracted several core parts of the ADT plug-ins into IDE-neutral libraries such that they are suitable for reuse elsewhere.
In particular, these are:
Our goal is to provide Eclipse-based tools, while enabling other vendors to provide first-class Android support in their tools. If there are other portions you'd like to see isolated, please let us know. See our feedback page to see how.