One short comment, from some-one who uses a priest as his main healer (although I have no experience with a shaman healer):

The spell I love the most from my holy/disc-priest is 'holy nova'.
Sounds funny, but with the glyph, which gives it 20% more healing, an instant, spammable group heal is realy fun, and I often do all my group healing with it, if the range is not a problem.

Other than that, I do my main healing with 'flash heal', 'renew' and PoM, 'Greter Heal' I normaly only use for healing individual members, if I can predict, that they get big dmg, so a 10k heal is needed and holy nova (or circle) wouldn't do it...

..and when the shit realy hits the fan, I occasionaly use 'Divine Hyme' or 'Tranquility' on my druid.

Spells of my priest I don't use regular (because I'm to lazy or forget about them) are: Lightwell, Gurdian Spirit, Desperate Prayer...