I use Roll20. They have fog of war, which is OK, and they have dynamic lighting. Dynamic lighting is brilliant - it shows what the character can see based on their positioning, whether they have darkvision, and what light sources are available.
My players tell me it adds to the paranoia and atmosphere and it becomes a lot more easy to get lost in a complex when you can't see where you have already been. So much so that the players have discussed designating someone to draw maps on paper as they go so that they are less likely to get in trouble if they have to flee.
It does take some setting up though - it's worth it to me.