The trouble with making healers awesome though is they end up being one man armies. In particular in 4th clerics were completely overpowered because they got powerful attacks spells that hit enemies but not friends - and also got to cast absurdly powerful heals with their minor actions. In my current game Ziggyny is playing a Shaman and they seem to be utterly nuts because their attack spells and utility are fantastic and worth playing on their own but when they can also cast heals that heal/prevent 37 damage with their minor actions... other classes seem pretty pathetic in comparison. It seems the same way in my Pathfinder campaign where I am playing a cleric. I have lots of good spells, good armour, great saves, good hitpoints and I also get to do extremely powerful AOE heals (2d6 at level 3) 7 times/day. I looked at the cleric class with the AOE heals removed and compared it to a wizard or sorcerer and concluded that I would still be extremely strong and given that I could still heal reasonably I would be welcome in any group. I then considered how good a character I would be if I had the AOE heals but none of the rest of my powers and decided that I would still be a good character!
So the current class design for healers in DnD seems to be that they are as good as any other class but get immensely powerful heals tacked on top. I don't much like this theory and I wish that the responsibility for healing was spread out around the party a little bit more. I really enjoyed the initial idea for 4th in which non healing classes were able to heal themselves by spending healing surges and that this plan would reduce the necessity for a healer in the group. It hasn't worked. In 4th edition the power of a healing surge needs to be substantially increased and the bonus that a healing class gives to the healing surge needs to be substantially decreased - probably reduced to zero. In that way the idea of people protecting themselves with the Second Wind action and using powers that let them spend healing surges makes a lot more sense and healers can be a backup system for the one guy who gets beat up really badly rather than the sole provider of super powered healing spells. I like the idea of a class that defends other people and heals them but I think the best way to make that work is a lot more of defending and a lot less of 'wizard who can also heal the entire party by themselves'.
When the Rogues, Wizards and Fighters can take care of themselves a lot of the time the Cleric can be a much more versatile sort of character and not feel like they are there just to help their buddies feel invincible and heroic. I also like the idea of being able to play when your healer can't show up - sort of like when somebody else in the party is away and things are trickier but manageable.