Most of the icons used here are from the Tango Icon Theme. Some of them have been modified.

showhide.png: Gnome Project (GPL) [http://art.gnome.org/themes/icon]
content.png: by PC <http://pc.de> (Creative Common v3) [http://www.iconfinder.com/icondetails/59552/32/cv_icon]
diffmode.png: by FatCow (Creative Common v3) [http://www.fatcow.com/free-icons]
unfilter.png: Everaldo Coelho (GPL) [http://www.veryicon.com/icons/system/crystal-clear-actions/]
heavy.png: Everaldo Coelho (GPL) [http://www.iconfinder.com/icondetails/15543/128/animation_fat_run_icon]
valid.png: Mark James <http://www.famfamfam.com/about/> (CC-by) http://www.iconfinder.com/icondetails/5880/16/active_check_green_ok_right_tick_icon
loading.png: by PC <http://pc.de> (CC-by) [http://www.iconfinder.com/icondetails/59192/32/loader_loading_process_spinner_icon]
openexternal: by FatCow <http://www.fatcow.com> (CC-by) http://www.iconfinder.com/icondetails/63957/32/card_export_icon