Every developer in the world knows that a picture is worth a thousand word, that's why they use icons to represent common actions, notification of important concepts, and also to illustrate their applications -- online or not. So we all agree that icons are essential. However we also agree that having beautiful icons is a definitive advantage since it can be used to attract the user's attention where we need it.

We carefully hand-picked some high-quality icon libraries for you, so you can use them in your daily work. As usual, make sure you read the license agreements, since not all the packages are free for professional use.

» Tango Icon Library

» InterfaceLift icons for Windows and MacOSX

» Social Bookmarks icons

» Famfamfam Icons

» Zeus Box Studio's feed icons

» Pixelgirl's icons

» Sphere Graphics icons

» GoSquared vector icons

» Pixelpress icon set (for mac, in .dmg format)

» Everaldo's YellowIcon library

We'll stop here for now, but we'll continue to update this post with new repositories as we find them. However we have a little tip for you: there are thousands of icon repositories on the web, many of which hold quality icons for MacOSX. Despite the fact that OSX uses its own custom format for storing icon definitions, there is a quick and easy way to convert that format to PNG. Of course, you'll need OSX... but that shouldn't be a major issue!