I am not talking about alcohol:)
Water, first and foremost.
Tea - herbal, Roibos can substitute from time to time (without added sugar).
The other drinks - coffee, green and black tea have caffeine, therefore should not really be counted for hydration purposes.
Milk is actually food. It can contribute but it's not the liquid of choice for this purpose.
Obviously, soups and other liquids also help, so do vegetables and fruits with high water content.
Carbonated drinks are just evil - best to stay away from them.
Fruit juices - they'd be fine in much smaller quantities - but it's obviously a better choice to eat whole fruits.
As for me:
I drink about 2-3 cups of coffee. I drink herbal tea most of the time, Chai (mostly in the winter) and lots of water. I never keep carbonated drinks at home - and really lost taste for them over time...