dev docs have some sample layouts and the Demos API is a great project.
, , , . layout_above , , android: layout_below = "id_of_other_bottommost_controll"
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<Button
android:layout_height="wrap_content" android:layout_width="fill_parent"
android:layout_alignParentBottom="true"
android:layout_marginBottom="10dp"
android:text="button"
android:layout_centerHorizontal="true"/>
</RelativeLayout>