pre 60+ holy/disc build?Follow

If you are going to solo from time to time, make sure to get 5/5 into spirit tap.. It's utter usefull while grinding.

Rest should be kinda clear I think.

http://www.worldofwarcraft.com/info/classes/priest/talents.html?000000000000000000000235051000320150000000500000000000000000000
(if you don't solo at all, just take out the 5 points of spirit tap.. but I don't think so =p)

Then you should most likely go for the "Divine Spirit" spell in the Disc-Tree to make ur Spiritual Guidance more powerfull.

http://www.worldofwarcraft.com/info/classes/priest/talents.html?504200013250012040000235051030320152000000000000000000000000000
By 70.. Again, if you don't solo, take out the spirit tap points. The first thing to go for after 41 woud be the 3 poitns in divine spirit and imp. divine spirit. So make sure to get them! After that - Well.. more mana and 4% more crit, everyone likes that I guess :P

Shadow will always be better for solo'ing. A PI/SoL build can be fairly good though, just takes *much* longer to get as good :P

First points into Spirit Tap, then towards SoL. Probably look like this.
Then start working towards PI. Of course, you won't be able to reach it without respeccing out of Spirit Tap. I'd do this some time in your 60's.
Final spec probably something like this. Holy Focus, Imp Mana Burn, and Martyrdom are pretty much entirely PvP stats by the time you hit 70, as getting hit much less crit in an instance pretty much means you die, and casters that you want to burn their mana usually have tens of thousands (too big to burn). If you don't intend to PvP, I'd trade those into Mental Agility/Absolution and Inspiration.