So, I mostly play bear and sometimes dabble in to cat. But over the various expansions I've played all the druid specs. With that said, there are folks who are much better moonkin around (hi bryn!), much better cat (hi Lilyria!), and much better healers than me. Hopefully some of them will jump in.
So lets talk about Bear stuff:
To start with, icy-veins is my default place to look:http://www.icy-veins.com/wow/guardian-druid-pve-tank-guide
Generally, if you are a bear, ilvl matters more on gear than anything else, except for slots without armor (neck/ring/trinket). Generally if given a choice, you want versatility & mastery. Leech is also remarkably strong. Versatility is slightly stronger than mastery, and gets even more so as you get more gear. I think crit is probably better than icy veins suggests and haste probably worst, especially for solo'ing or lower-geared bears - but regardless, versatility & mastery are better than both. For a rough comparison, I'd suggest adding versa+mastery+leech and then half of crit+haste+agi. Trinkets are just weird - some of the ones with damage shields are really good as they benefit from mastery. No one has done particularly good trinket analysis except at the mythic level -- and a bunch of the world quest and dungeon trinkets are obtainable at high enough ilvl to be competitive in everything but mythic raiding. But it means none of the sites that list gear have anything close to a useful ordered list of trinkets.
Standard bear rotation is: Moonfire (if you took galatic guardian and it proc'd), Mangle, Thrash on cooldown, Moonfire to maintain the dot, Swipe. For AoE packs (4 or more), swipe starts being more damage than mangle - but doesn't provide the rage mangle does so you don't want to drop mangle from your rotation if you are getting hit hard enough to want to maintain ironfur. Any attack except mangle, has a change to reset the cooldown on your mangle. Mangle both generates extra rage and is the key that some artifact powers trigger off of - so generally you want to mangle as much as possible. Since 2 (3 w/galactic guardian sort of) of 4 abilities are AoE, this means Bear has a lot of AoE. It also means we don't have the huge threat lump up front like the tanks which are resource rather than cooldown constrained (DH, DK) have.
Subtle things bears are good at, some of which require practice to do well:
* Taking sustained magic damage - mark of the ursol is 30% reduced magic damage. Once you get a reasonable chunk of artifact talents, the duration increases and you can basically keep this up 100% of time (at the cost of not keeping ironfur up). But for fights where one tank is soaking magic damage, its very useful to remember.
* AoE pickups and damage - we can spam aoe moves constantly. With the correct spec, bears can do dps almost as good as a dps during AoE phases.
* Mitigating large purely physical hits - if we pool our rage, we can possibly have 3 stacks of ironfur up which is +300% armor. This isn't sustainable or always reliable, but there are times when you can pull it off instead of using a cooldown. Very useful for fights where you feel like you need more cooldowns than you have.
* Recover from large hit raid mechanics - frenzied regen is cheap and heals you 50% of the damage taken in the last 5 seconds. Which means if you save a charge for when you are about to take a huge hit, you can often heal it. Note this double dips from your mastery bonus - larger health pool means you can survive a bigger hit and the healing is increased. Since it has 2 charges, I often use 1 charge and then keep the second in reserve waiting for a large hit. The rage cost is low so you can afford to just use it any time your health dips suddenly.
* Being really mobile. If you take "Wild Charge" and "Feral Affinity", combine it with skull-bashes short range charge and stampeding roar and the occasional cat form sprint, and you end up being able to move fast and have multiple charges. No tank is as mobile as a bear can be. (Admittedly, this requires taking talents to support being mobile.)
* Making healers look good on the healing charts - our mastery increases our max health and the size of incoming heals.
I'll share two weakaura sets I have for bear later. One set is a box that includes all the bear cooldowns/buffs and shows the running duration. This is very useful for tracking things like stacks of iron fur and duration of mark of ursol. The other set is a box that includes all the bear cooldowns and how long until they come off of cooldown. I put the first box to the left of where DBM displays active warnings and just below where I've move my target & target of target boxs - making it very easy to monitor the buffs. The second box is to the far right, just to the right of where DBM displays things that are coming up. I honestly look at this less, but it is useful sometimes when I'm worried if I'll have a cooldown up for a some mechanic since I can look at DBM & it at same time.
So I have mixed feelings about icy-vein's suggested spec - especially for solo'ing and small raid / non-mythic raid content.
Tier1: I recommend brambles. It doesn't scale up as enemy damage does, but its good free passive damage and damage reduction. Its great for solo'ing & trash. And its a noticeable amount of healing even on bosses. Bristling fur requires careful timing (and can be negated by an unlucky lucky-dodge streak) and blood frenzy requires a bunch of mobs to be really useful.
Tier2: Wild Charge is really strong if you use it. Its a lot of mobility. If you don't want to manage using it, guttural roar halves the cooldown of stampeding roar. Icy-veins says use roar but I prefer charge.
Tier3: Icy-veins says take resto affinity for free healing, but I recommend feral. I've found for any fight where you need to move or get out of stuff, the extra speed from feral affinity is great. Its hard to capture in raid logs, but the ability to more reliably get out of things you aren't supposed to stand in is huge. Also, really nice for solo'ing.
Tier4: Whichever. I run with typhoon sometimes, bash other times.
Tier5: Galatic Guardian. This is good damage on big AoE packs (since each swipe/thrash might trigger several moonfires), and really solid damage on single target and generates extra rage. Incarnation has specific uses around either needing 3 targets dead fast, or needing burst once every 3 minutes - but not in current raid content. But Galatic Guardian is good all the time.
Tier6: Guardian of Elune. Again there might be special cases for "Survival of the Fittest" but I've not found them yet.
Tier7: Rend and Tear. There are special cases for Lunar Beam. It might even be good if you are solo'ing and feel like you need more self-healing.
And as a final personal preference - I like accumulating a set of gear that is +speed. So much of solo'ing is spent running around and being able to do that much more quickly often outweighs the lost ilvl. It also lets you do things like pull to much, and then kite them as thrash & moonfire drain the mob of 20 adds trailing behind you (and it gets to be a fun art of strafing through them reapplying thrash's slow and then getting out of melee range again). Its also amusing that with a bit of speed gear and feral affinity, cat form sprint is faster than a ground mount. So running around dalaran is just that much more convenient as a druid... (And using the fishing raft in stag form, over water gets faster than flying mounts...)