Icons, Pictograms and Symbols play a very important role in everyday life and especially in software, web design, user experience design and user interface development. During the normal course of a day everyday a user with a quick glance identifies a stop symbol, no parking board, restroom etc. The same rules apply in web development, users associate certain icons and symbols with common tasks and services which they use on a daily basis. While designing ZetaLight I made use of a few pictograms for the main menu on top and for the blog posts.While using the icons I researched the best freely available vector icons. I have made a list of them below.
Glyphish Icons for iPhone & iPad apps
Created by Joseph Wain and shared under a Creative Commons Attribution license. Designed and carefully optimized for use on toolbars and tab bars in iPhone & iPad apps, they’re also perfect for Android apps, websites, t-shirts, tattoos and more.
Iconic Icon Set
Iconic is a minimal set of icons consisting of 114 marks in raster and vector formats — free for public use.
One main goal for these icons were to have them maintain high legibility over a large scale range. Most of the icons in this set will work from 8×8 pixels to however large you need to go. To give the greatest flexibility, the icon set packages all icons in PNG, SVG, SWC and Omnigraffle stencil formats. Iconic tries to work with various tools/workflows to make your life a bit easier.
The Android Icons package includes 30 PNG menu icons plus the additional source files for further customization.
Token Vector Icons Set
Simple and minimal, Token was created as a sequel to Mnml and was originally designed to add uniformity to Windows 7 taskbar. A bunch of very commonly used applications and tasks.
Pictoico: scalable vector Pictograms
Full preview of over 100 hand crafted unique pictograms available for free download. Over 100 fully scalable pictograms/icons free to download. You’ll love their simplicity, while at the same time improving project’s usability. Use them in your online, print, mobile and software applications. They will work good even for signs in real world around your street, campus, resort or even city: possibilities are unlimited.
Vector Social Media Icons
This free set includes 50 icons of the most popular social media networks on the internet. The icons are designed in 32px and 16px vector format. With the vector format, you can scale the icon to any size to fit with your design or use it in high quality print materials. What you will get from the zip package: 32px and 16px in three different file formats: vector EPS, PNG, and GIF.
Download Vector Social Media 
A bunch of various different vector icon sets.
The complete set of 50 passenger/pedestrian symbols developed by AIGA is now available on the web, free of charge. Signs are available in EPS and GIF formats.This system of 50 symbol signs was designed for use at the crossroads of modern life: in airports and other transportation hubs and at large international events. Produced through a collaboration between AIGA and the U.S. Department of Transportation (DOT), they are an example of how public-minded designers can address a universal communication need.
These copyright-free symbols have become the standard for off-the-shelf symbols in the catalogues of U.S. sign companies. They are now available on the web for the first time.
Other Vector Icons Pictogram, Symbol Sets
- 30 Free Vector Icons By Dezinerfolio. Download Icons here .
- BrightMix Vector Icon Set. Download Icons Here 
- 108 Mono Icons: Set of Minimal Icons By Jason Cho. Download Icons here .
- Simple & Bold Social Media Icons By WooThemes. Download Icon Set Here .
- Symbol Signs collection By designworkplan. Download Icons Here 
- Map Symbols & Patterns for NPS Maps. Download Icons Here 
- 165 Lovely Vector Icons by gosquared. Download Icons Here 
- Web 2.0 Services Icon Package By uberpiglet. Download Icons Here 
- Picol Pictograms. Download Picol Pictograms 
- Ecomo Pictograms. Download Pictograms here 
- Collection of 27 authentic warning signs. Download Warning Signs here