Ok lets begin.
My only character is a Holy Paladin. Level 80.
Paladins dont have 3 or 4 Spells to heal with.. thats bull ****.. Paladin healers are actually very very fun.
Let me give u a list of spell.
-Judgement of Light ( Which does heal you )
-Holy Shock.
-Flash of Light.
-Holy Light.
-Beacon.
-Sacred Shield. ( Now if you have taken the right talent.. If you place Sacred Shield on someone and use "Flash of Light" It will then heal over time. If the bubble is activated you then can crit 50% on anyone with Flash of Light.
-Glyph of Holy Light ( This will AOE Heal up to 7 Raid members. )
-Lay on Hands ( My favourite spell.) this is because it gives a crap load of mana back if you have the right Glyph.
-Most Talents for holy offer High Crits and Instant cast's Which is awesome because paladins are big healers.
<Your Seals also offer a veriaty of things.. Eg Seal of Wisdom gives you mana.>
You Must stack Intellect Gems.. You will find Paladins usually have the most mana out of any class. Even a Mage.
A paladin is know for its big heals which is nice like f0xZA said: "Its quite satisfying to know you can top off that 50k hp tank that pulled half of HC HoS in two casts."
In my opinion Paladins are single target healers and and are always needed in raids.
http://wow-heroes.com/ Take a look at my paladin, His name is "Noobieless" on the server "Darkspear" EU
Hope this helped