This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
1. Assuming that you have only a ListView and a button to display in your activity. Say you use LinearLayout; you can set the layout_weight of the ListView to "1" and then have the button below the ListView.
2. If you are using RelativeLayout you can use align_parentBottom property to place the button at the bottom of its parent