discovery.png - LGPL - http://www.iconfinder.com/icondetails/18227/48/browser_map_navigation_navigator_icon
home.png - Free for personal use only - http://www.iconfinder.com/icondetails/51304/128/black_house_home_house_icon
system_monitor.png - Free for non commercial use - http://www.iconfinder.com/icondetails/23964/48/monitor_system_icon
warning48.png - GPL - http://www.iconfinder.com/icondetails/2479/48/messagebox_warning_icon