I am using a free flash application called DodontoF, which can handle battle-grids, counters, initiatives, dice rolls and such. All the players need is a browser which can handle Flash. So it does not matter if a player is using Windows, Unix or Mac. Unfortunately, all of it's menus are in Japanese language, as the creator is Japanese. I guess similar tool should be for English players.
I am using DodontoF for solving combats, showing long descriptive texts, images and such. And using Skype for conversation. It will make online game session much faster than when using text-chat.