My way of the priest: Fuck what everyone else says
 

So everyone says you have to go shadow to solo a priest, and that you have to go holy to do good in instances. Everyone says spirit sucks. They're all wrong.
At lvl 50 my priest is full discipline +5 in improved renew and +5 in spirit tap with about 90 base stamina, 140 base intellect, and 301 base spirit (+29 with my own buff), and it's great. When I'm soloing and I kill something, I just wait 15 seconds (spirit tap gives 15 seconds of double spirit after a kill) and most of the mana I used is back. In instances, I can keep two people renewed indefinately and if more is required, my mana still lasts a long time. I regen 97 mana per tick normal and 15 while casting (That's 538 mana between pairs of renews). Except for rebuffs and boss fights, I hardly ever need to drink in an instance.

Could I be more efficient at healing or soloing? Probably, but this spec is very good for both, which is really what you want allong the road to end game.

Spirit Tap kicks ass, especially since I mainly attack with magic unless the enemy's HP is near critical. It was the first talent I put my points into. Ah lurve mah Priest. :D

WW, you have to go shadow to solo as a priest. For instances you have to go holy. Also, spirit really fucking blows.

With a standard Int/Sta build, Spirit Tap is okay. With a Spirit build, Spirit Tap is like drinking whatever drink the monsters your level are dropping.

Who says you have to go Shadow spec to solo? I went from lvl 1-60 with just discipline/holy :P. It's not SMART but it's possible ;).

As far as mana regen ...mana regen is great for big boss fights and it's all the rage now ;). That and +healing equiptment. Not quite sure what the max +healing you can get but the more the better I suppose :P.

Critting Greater Heals over 5k makes me happy, especially if the MT was at like 1K life. ^_^

Never had any complaints about my healing. Spec doesn't matter the most if you aren't an idiot.

Spec matters if you're solo healing a Tank for a long fight, it's all about efficiency.

I'm specced for Greater Heals, so I rely on Spirit, +Healing, and a large mana pool in case my regen cycle gets broken by a crit or two.

:p