There is a 102 royalty free website & GUI icons set in various formats from Iconblock that can be used for both personal and commercial purposes.

iMac 27 Icons by Svengraph from deviantart.com includes .png, .ico, icns with size: 512x512, 256x256, 128x128, 64x64, The icons are free for personal or commercial use, but cannot be re-distributed or sold as your own.

Here is 2 free Google Buzz Icon set and 1 PSD Vector including the pack that i find it from web to create your own cool Google Buzz icon to share your website articles on Google Buzz.

E-Commerce Icon Set inclides Products on Sale, New Porducts, Checkout, Secure Payment, Credit Cards, Delivery, Shopping Bag, Empty Shopping Bag, Shopping Cart, Empty Shopping Cart in PNG format with 128, 64, 48, 32px. You can use these icons on your E-Commerce Online Store.

Free Mobile Icon Set includes Phone Call, Photos, Messages, Calculator, Wireless, Calendar, Settings, Contacts, Notes, Map in PNG format with 128, 64, 48, 32px. You can use these icons on your mobile applications or mobiles.