More and more websites are starting to use Font Glyphs or Font Icons. They're easy to make, easy to pick from and their incredibly light weight compared to independent images or even sprites.
What are the major advantages of using Icon Fonts?
They are vector, which means they can scale indefinitely without losing quality
They are lightweight
They are supported by every browser
You can add almost any thinkable text css to them (shadows, colors, rotation, gradients)
Takes fewer HTTP requests to your server = less load :3
So what are disadvantages of using Icon Fonts?
Screenreaders may misinterpret fonticons, reading them out loud
DUSTY OLD BROWSERS cannot render font icons. But really, who uses IE7 anymore.
You can only serve font icons in a single color -or- in a gradient. No fancy multicolor rainbow awesomeness.
Firefox sometimes renders icon fonts with a larger font-weight (bolder), so they may look differently on there.
The top list of FREE icon Fonts
Foundation 3 - 283 beautiful icons with rounded corners
Font Awesome - 439 icons in a constantly updated icon font
Google Material Icons - Over 200 icons by google.
IconSweets - 60 icons by YummyGum (has a paid v2)
IcoMoon - 450 free beautiful icons, with editor on site if you want to pay
HeyDings - 60 pretty awesome webfont icons
Open Iconic - 223 icons in a lightweight and beautiful package (.woff = 12.4kb!)
Sosa - 160+ icons
Glyphish - 200 free icons (you must provide credit), also has a paid version of $100 for over 1500 icons
Glyphicons - 470 free icons and 50 free social icons
Batch - 300+ icons for use on the web and apps, now free
Brankic1979 - 350 pixel perfect icons, scalable to any size
IconMinia - 139 vector icons
Octicons - by GitHub, usable in any of your projects
So there you have it, pretty icon fonts for free, available for you to use in your projects. Most come with a handy-dandy instruction page aswell. If you have any additional icon fonts and you would like to see them back on this list, do not fear to comment down below!