Given the original topic was never formatted to be a sticky in the first place (only an afterthought), I decided to start a new one that doesn't require reading through more than 40 pages to come up with answers.
This is first, and foremost, a Discussion. A lot of this is opinionated, and in some cases may be flat out wrong. Bringing information and communication together is the point of our forums, especially our stickies. If you have something you'd like to add, it can definitely go here. It will also change as both content, and the voices of the community adapt and grow.
Just for the sake of simplicity, here's the revamped level 80 talent builds with glyphs, and explanations where possible.
This is a completely open discussion. The only point of this new guide is "having answers from clicking this link" more than anything, as well as being able to patch-date-stamp the ideas here.
Let's get started:
~Last update, 3.3.3
PvE
Shadow:
Given Shadow's focus as a damage dealer, it's pretty simple on its build.
Basic Shadow Build
Improved Spirit Tap offers roughly the same, if not more, mana return as Focused Mind does. But its increase in Spirit also equates to more damage done. Improved Vampiric Embrace is not carrying your healers, it (coupled with Dispersion) can let you live through damage that should've killed most people, otherwise. It also lets you act as a mobile Healing Stream totem, and the added utility shouldn't be overlooked.
Glyph of Dispersion offers more mana than Glyph of Shadow Word: Pain, as Pain takes nearly than a minute to even pay for itself. On certain fights, it allows you to be able to support yourself through extensive damage more frequently. These happen, and not just because "lol u must be bad". Glyph of Mind Sear is popular on some fights that you can actually use it as well.
4pc10 Shadow Variation
This is a spec I threw together, with the 4pc10 set bonus in mind for dropping Mind Blast from priority. Picked up a few fun utility talents, including an interrupt, Inner Focus for Divine Hymn (as needed, also works on Mind Flay).
~Disclaimer: I don't have the stats or latency suggestions that would be recommended for doing so, just the ideas being thrown out there. Be sure to read the shadow guides (or this post) for this information
Discipline
Standard Discipline Build
Variations include swapping points from Divine Fury into Spell Warding, specifically for most of ICC's spell damage fights (all except Saurfang?), and 1-2 points from Holy Specialization for Healing Focus, depending on if you run with a Holy Paladin that has Improved Concentration Aura or not.
Greater/Haste Discipline Build
Picking up more stat itemisation allows a shift from Flash heal to Greater Heal when needed, as well as tossing out a Prayer of Healing every now and then.
Both of these have an open third glyph. The Flash Heal glyph is not recommended for either, considering the mana cost of Flash Heal is not your problem, its the use of your other spells. If you find yourself tank healing in 10's, or moving frequently, Renew may be a prime choice for when you can't Shield and Mending's on cooldown. Otherwise, and most often in 25's, you should grab the Prayer of Healing glyph for some outgoing hasted support.
Holy
Standard Holy build
This build has room for three points, and one glyph. The first point is usually a toss up between Lightwell, Inner Focus, and the last point in Blessed Resilience. If your raid can click Lightwell, it's great. If not, then obviously it's a waste of a point. Inner Focus can be useful. But if you're only using it for Divine Hymn, it's a waste of a point. It needs to be used to make it useful. If not, just run with Blessed Resilience, and enjoy the extra mileage.
Most Holy Priests at this point in the game will stick the other two of those points into Body and Soul for added utility (as its usefulness really is only limited by your imagination), and their Discipline counterpart is doing more than just spamming shields frivolously.
Another option would be to put 2/5 into Empowered Healing for stronger Flash Heals, which is fine. 2/5 and 3/3 Blessed Resilience will always outweigh 5/5 Empowered, though, remember that. 1/2 Surge of Light is enough, and you should never run without the Guardian Spirit glyph.
Variations:
-2/2 Healing Focus is based on whether or not you have a Holy Paladin with Improved Concentration Aura or not. If you do, go with 1 point.
-Spell Warding vs Divine Fury is your call, depending on your preference.
-The last point of Holy Specialization (or possibly Spell Warding, if it's in your build) could be dropped for Desperate Prayer. It's not required by any means necessary, but a few priests (myself included) often find it a great button to push when needed (especially when all of the above are just filler talents anyways).
-A tank healing variant would have you dropping Surge of Light (and up to two points of Empowered Renew) to pick up Empowered Healing (2 points) and/or Inner Focus. This is recommended for two-healing 10 man hard modes, where you need to fill the gaps in tank damage as well as shift to raid damage at will.
The third glyph slot is open to either Renew or Prayer of Healing. Flash Heal's mana cost should not be your biggest drain, if you're casting it enough to make a difference on your bar, you should probably look at your playstyle.
Prayer Build
This build is a heavy-aoe specific build. You would not be casting Flash Heal at all, so Serendipity and Surge of Light are both considered "useless" talents here, thus dropped in favor of Mental Agility. Note: This is not a recommended build for anything with the exception of Aura Fights or Arthas, at high haste values.