RPGtonight is a free online virtual tabletop site that works in your browser: There is nothing to download, just get on and play. Features include a dice roller, a map display with moveable miniatures, grids, and fog of war, non-map image
display, built in text and voicechat, a sound player (for sound effects and background music), customizable character sheets, a growing online collection of over 1000 miniatures (tokens) about 300 sounds, and several dozen maps, plus storage space for your own maps, images, minis, and sounds.
The site is non-system specific. We have tried to make it flexible enough to handle any role playing system.
RPGtonight is actually the first step towards a planned online, real time "living game." However, when that gets going the site will still be available for playing your own games. It's continually being improved, and is about to undergo a major upgrade to the sound and map features.
The address is www.rpgtonight.com If you want to try it out, all you have to do is sign on, create a gameroom, read the instructions, and play around with the features.