First off, don't level with your endgame build. Whatever build you do level with, make sure it maximizes Spirit Tap (Improved Spirit Tap is not necessary if you aren't going Shadow). If you decide to level Holy, get the Smitey talents (Searing Light, Surge of Light, Holy Reach) while leveling.
You can heal just fine with any leveling build at least up to Northrend. Just how high off-spec healing goes is a topic of debate. Experiment and spec however it's fun for you.
For endgame PVE, if you intend to be Holy for surely sure, here's my personal lowdown on talents:
Most everyone has: Improved Renew, Holy Specialization, Divine Fury, Inspiration, Improved Healing, Spiritual Guidance, Spirit of Redemption, Surge of Light, Spiritual Healing, Holy Concentration, Empowered Healing, Serendipity, Improved Holy Concentration, Circle of Healing, Divine Providence, Guardian Spirit
Hardly anyone has: Spell Warding, Blessed Recovery, Searing Light, Blessed Resilience
Depending on personal preference/playstyle/role, most will then choose between: Healing Focus, Desperate Prayer, Holy Reach, Healing Prayers, Lightwell, Test of Faith
Those are all in order of tier on the Holy tree. Holy builds will generally have 14 points in Disc (usually Twin Disciplines, Improved Inner Fire and Fort, Meditation and Inner Focus).
Last I saw, Elitist Jerks liked
this build.
I run with
this one.
However, if you're saying you're going Holy only because you want to heal and you think that's the healing spec, I suggest playing with both deep Holy and deep Disc once you're high enough level to really give both a shot. Both are viable for 5-man, heroic, and raid healing, but they're pretty different playstyles.
Grain of salt: this is all my personal opinion. I'm not superpriest or anything.