Useful Segoe UI Symbols
… compiled list of symbols that can be used to copy Windows 8’s style:
Developing Windows 8 – Using AppBarCommand Icons outside the AppBar « Matt Duffield
One of the things I really like about developing Windows 8 applications is the ability to use the built in icons provided by the Segoe UI Symbol font.
Windows 8 Metro apps – a lot of icons are available out of the box ! | Jonathan ANTOINE's thoughts on WPF, Silverlight, WinRT, NUI...
Windows 8 AppBarIcons enumerated and visualized
Download: http://www.flickr.com/photos/adamkinney/6952800759/
Apple OS X Lion Buttons in CSS
Symbols, Buttons and Icons For Free | Smashing Magazine
We love free icons and icon sets. In the overview below we present 55 more 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 free in your private projects. Nevertheless, it is always worth to take a look at the license agreements — they can change from time to time.
Buttonator
drag and drop icon/button maker