IOGear GKM681R 2.4GHz Compact Wireless Keyboard with Trackball for $17.99 shipped after after this $12 rebate.  Here is a screenshot for your reference.  This is a 2.4GHz wireless compact keyboard with built-in optical trackball and works well for a home theather PC (HTPC).  Most places have this wireless keyboard with trackball for about $29 and more.