Iconoir is one of the biggest open source libraries with currently 914 SVG Icons. No premium icons, no email sign-up, no newsletters.

550+ Highly customizable free SVG icons (MIT licence) https://github.com/tabler/tabler-icons

… delightful, beautifully crafted symbols for common actions and items. Download on desktop to use them in your digital products for Android, iOS, and web.

access core functions on Android, iPhone and Blackberry using JavaScript - phonegap/phonegap

… a free Photoshop resource that makes it easier for you to make icons. Edit a single object and it’ll automatically render out all the various sizes required on iOS & Android. Build in textures and colors make it easy to get started and the bundled actions make exporting a breeze.

(Here’s what it looks like)

The Icon Handbook is a reference manual, how-to guide and coffee table 'showcase' in one. learn how to design icons for interfaces

an edited excerpt from Chapter 3 of «The Icon Handbook» by Jon Hicks

Free design resources layered PSD, resizable vectors, PNG icons

Round-ups of beautiful and useful **icons** are almost legendary here, on Smashing Magazine. While some readers complain about the annoying "list"-style of some of our articles, we are confident that useful round-ups of relevant resources are very valuable and useful for designers. This is why over months we collect useful links and then present them in posts in the magazine. Like it or hate it, but the feedback that we get from the design community when we publish such posts is mostly positive which is why we keep doing it.