I find that I want priests to splash their fortitude around in towns when I'm on my warrior or rogue, and that it would be nice if mages would hand out free water to my priest because it's so expensive for just one stack at 70 (2 gold 56 silver) and Dusty's always running out.
So I started trying to be a ton more generous on both my priest and mage, offering water to priests if I see them, buffing classes with mana, and using Dustfire to fortitude people, especially classes that can't use intellect buffs.
The only class I am reluctant to buff or give water to is hunter, because I honestly don't think they need it. They're the strongest class while leveling, they easily track and kill their opposition, and they can just set their pet on a target and auto-attack while their mana regens.
My question, though, is what does your class seem to always need from another class but you never get?