Skype for voice communications, which is so much better than having to type things out. Being limited to five players on a confrence call isn't a bad thing either, since I limit the size of all my games.
Dice rolling isn't a huge deal, but it would speed things up to have it done by a program.
The most important thing is being able to share maps and pics. Where the players are located and where the npcs are is huge during fights. It was the biggest point of confusion during combats on Muxes and Mushes, players and admins were sledom on the same page and it resulted in considerable problems.
This whole concept fo playing online is really growing on me and I already have a couple of players interested.