Roll20

Roll20 is the free, easy way to play tabletop games (such as pen and paper RPGs) online with others. It’s completely web-based, so it runs right in your browser. It supports video and voice chat, background music, character sheets, a massive art library, and more!

Elegantly Simple.
Roll20’s virtual tabletop, Compendium, and Character Building tools are powered by HTML5 technology and run directly in your web browser. There’s nothing to download or install and no messy configuration files for Game Masters or players.

Storytelling, Enhanced.
Roll20 gives you ways to enhance your own unique storytelling games via drawing tools, simple handouts, secret whispers, background music, and other real-time shared elements.

System Agnostic.
Roll20 doesn’t favor one set of mechanics over another, so it can be used with a variety of games. Play D&D online (any edition), Pathfinder, Shadowrun, Savage Worlds, FATE, board games, and more

Easy to Use
Being a game master is hard enough. Roll20 makes it easy as possible saving you the hassle of installations or configurations. Simply open Firefox or Chrome via Windows, Mac, or Linux and start via your browser.

Many more powerful features:

Character Sheets
Dynamic Lighting
Video + Voice Chat (Including Google+ Support)
Dice Rolls (3D + QuantumRoll)
iPad + Android Apps