icon sites

Find Icons.com
great site: lots! of free icons, groups of single images. not easy to find what you need.
findicons.com/pack/2395/credit_card_debit_card_and_payment_icons
findicons.com/pack/95/muku_style
iconarchive
this is where I found the Google icon
mr icons
this is where I found the GoogleEarth icon
SoftIcons.com
seems well organized

Very Icon.com

iconfinder.com
good, huge selection of free icons.
http://www.awicons.com/free-icons/