Roll20.net is an online system that allows for battle maps, sharing of resources, enables video chat and everything for a fairly comprehensive online D&D roleplaying experience online.
The invite link to join the current campaign is: Roll20
You will be required to make an account and all that stuff, as long as you're in MY game, you will see no ads or anything. If you don't plan on playing online ever, you don't have to bother with this.