How does one obtain a collection like this? Amazing.

120+ Free Ajax Activity Indicator Gif Icons from Badeziner

Free for personal and commercial use.

Fineicons.com

I usually use Iconlet but ICONlook looks quite awesome with the tag cloud and displays the icons by popularity.

This one is from Russia!

Free of Charge RSS Feed Icons from Malevi4

Ever wondered how the great icon designer do it? Well, here are 15 Photoshop Tutorials that lets you peek behind the curtain and get you started.

If you want to learn how to design icons like a ninja, check out Icon Resource (not free by the way).

Want to be an Icon Designer? 15 Amazing Photoshop Icon Tutorials. from Speckyboy

Professional edited free vector arrow symbols & icons for personal and/or commercial usage. This collection of arrow symbols can help you in your art & design. Arrows are often used in Signage and Wayfinding design to guide a visitor in the right direction. All 56 arrows are drawn by Sander Baumann with Adobe Illustrator and can be used in many different ways.

56 Professional Free Arrow Symbols and Icons from SEGD

In the overview below we present 40 excellent, free and professional icons for desktop and web design. Some of them can be used for both private and commercial projects. You may always use them for fre in your private projects. Nevertheless, it is always worth to take a look at the license agreements — they can change from time to time.

40 Professional Icon Sets For Free Download from Smashing Magazine

At Frexy, we really love icon design. In the past few months, me and Vu Tran have worked on an icon set called “Bright!”, and today, we happily release Bright! as a freebie for you.

Bright! - A Free Icon Set by Min Tran

Credit card icons are an essential part of every online-shop. They are often used to indicate available payment conditions and purchasing options. The clearer they are presented in the online-shop, the easier it is for potential customers to figure out if they actually can pay online in this shop. Therefore when it comes to the design of an online-shop there is no way to get around using some credit card icons.

Free Credit Card Icons For Online-Shops from Smashing Magazine

Onur Oztaskiran of Monofactor is giving away this sexy vector set for free. What a guy! And by the way, he's making more..that's just awesome.

Free Vector Icon Set 1 - Containing 25 Icons

“All you need to add a Favicon to your site is a Windows Icon (.ico) file called favicon.ico that you upload to the main directory of your website...Some browsers will look for a direct link in the HTML source code to your site's favicon.ico file. You can help these browsers by adding this link in the head section of each page on which you want the Favicon.ico to appear.”

Mysteries Of The Favicon.ico — How To Create A Favicon In Photoshop

1. Insufficient differentiation between icons
2. Too many elements in one icon
3. Unnecessary elements
4. Lack of unity of style within a set of icons
5. Unnecessary perspective and shadows in small icons
6. Overly original metaphors
7. National or social characteristics not being taken into account
8. Images of real interface elements in icons
9. Text inside icons
10. Outside the pixel framework

10 Mistakes in Icon Design by Denis Kortunov

Update: also check out Apple Human Interface Guidelines for some icon design insights.