With a lot of new enchants people might not know what kinds of enchants there are and what is best. Most this information I got of rawr, but I doubt rawr a bit because some real necessities like Hit rating for cat does not score that high, nor does expertise for bear. Armor however scores pretty high where in my opinion that is something a bear druid should not get extra of by enchants, though for this moment I will trust rawr.
I would like your input on what you think is best. I will change the list where and if needed. All enchants are from a PVE point of view.
I know enchants are depending on your current gear. In bear, if you have 40k health a lot of other enchants would be much preferable vs a stamina enchant. I made this list from the standpoint that all stats are needed equally. I have stated the next best alternative(s) if valid between ( ) behind the "best" enchant. The alternative will however never be a lesser version of the best one. A 15 agility enchant is not the alternative to 20 agility enchant. An alternative, if any, must contain a different stat.

This list also does not include the enchants that are best for dual roles. Say you only have one ilevel 200+ gloves you use for tanking and no alternative to specifically use for dps. The agility enchant might be preferred here because it is good for tanking and dps. This post does not hold that kind of information.

Where possible I added item links to WowHead.com to make it possible to see the enchant. This results in some enchants being linked as enchanted on a scroll, which might be difficult to read against the light background. My apologies for that.

Any comments?
[List adjusted: 3.1.3 ->17-06-2009]
Rawr used: 2.2.6 (With my current gear of course)

Bear

Head: [Arcanum of the Stalwart Protector]

Shoulder:[Greater Inscription of the Pinnacle] (Greater Inscription of the Gladiator - Spell - World of Warcraft *)

Back: [Scroll of Enchant Cloak - Major Agility] ([Formula: Enchant Cloak - Mighty Armor])

Chest:[Formula: Enchant Chest - Powerful Stats] ([Scroll of Enchant Chest - Greater Defense] / [Heavy Borean Armor Kit])

Bracers: [Formula: Enchant Bracer - Major Stamina] ([Scroll of Enchant Bracers - Greater Stats] / [Formula: Enchant Bracer - Major Defense])

Gloves:[Scroll of Enchant Gloves - Major Agility] ([Glove Reinforcements] / [Heavy Borean Armor Kit])

Pants:[Frosthide Leg Armor]

Boots:[Scroll of Enchant Boots - Superior Agility] / [Formula: Enchant Boots - Tuskarr's Vitality] ([Scroll of Enchant Boots - Greater Fortitude])

Weapon: [Formula: Enchant Weapon - Mongoose] ** / [Formula: Enchant Weapon - Blood Draining]([Formula: Enchant 2H Weapon - Major Agility])

Note:

* If you really need stamina (Sarth 3d for example) though the resilience is worthless.

** It can be disputed which enchant is the best, Mongoose's high procs or the constant factor of 35 agility. Rawr shows mongoose to be the best though.

For tanking expertise is a real nice stat. It reduces the chance the boss will parry you and by doing so increase his damage.
A lot of gear has expertise but you will need about 14% (?)* to get the "cap" (some bosses have higher parry chances).
Note:
* The exact parry cap is debated, but it is believed to be somewhere around 14%. This isn;t really THAT important though. Expertise cap is in my opinion not something to go for. Keep in mind though that the expertise soft cap of 6.5% is close to a must on expertise.

The interesting enchants to look at are:

Expertise enchants

[Scroll of Enchant Bracer - Expertise]

[Scroll of Enchant Gloves - Expertise]

Note:

Expertise enchanting is very costly. Rather choose expertise gems over enchants. Example: 1 gem can have 16 strength, 16 agility, 16 expertise rating or 32 AP. Per class it differs what is most useful. However, point wise they represent the same. Meaning 1 agility equals 1 expertise equals 2 AP in value.

Now you can either enchant 15 expertise on a glove or put 20 agility in there or 44 AP. (For druids 20 agi > 44 AP at the moments)

For bracers you can ether enchant 15 expertise or you can put 50 AP on it.

The reason for this is that the expertise enchants are pretty low level enchants versus the other higher level enchants. This means that if you need 15 expertise, you rather replace a 16 agility gem with a 16 expertise gem, then replace your 20 agility glove enchant with a 15 expertise enchant.

Cat

Head: [Arcanum of Torment]

Shoulder:[Greater Inscription of the Axe]

Back: [Scroll of Enchant Cloak - Major Agility] ([Formula: Enchant Cloak - Greater Speed]) *

Chest:[Formula: Enchant Chest - Powerful Stats]

Bracers:[Formula: Enchant Bracers - Greater Assault]

Gloves:[Scroll of Enchant Gloves - Major Agility] ([Scroll of Enchant Gloves - Crusher])

Pants:[Icescale Leg Armor]

Boots:[Scroll of Enchant Boots - Icewalker]** / [Scroll of Enchant Boots - Superior Agility] ([Formula: Enchant Boots - Greater Assault])

Weapon: [Formula: Enchant Weapon - Berserking]***, [Formula: Enchant 2H Weapon - Massacre]

Note:

* TBC's "Greater Agility" might actually be better then the haste one.

** Only the best if you are not hitcapped yet (see below)

*** Berserking seems better, but since Predatory Strikes is also applied on the 110 AP enchant it makes Massacre a bit better. The Berserking enchant will not give your Weapon extra AP, it will give you an extra Ap buff that is not affected by Massacre.

It is also important to have hit rating as cat. There is not much hit on items (I myself find I want 4 times the hit rating I have). So if you are looking towards hit rating you could choose some of those enchants:
[Currently outdated, I am bursting with hit and I want expertise, though still goes for people with not as much hit on their gear).

Gloves: [Scroll of Enchant Gloves - Precision]

Boots: [Scroll of Enchant Boots - Icewalker]

Weapon: [Formula: Enchant Weapon - Accuracy]

Depending on trade skills it is possible to get different/most likely better enchants.

Bear

Shoulder (inscribers only): Master's Inscription of the Pinnacle - Spell - World of Warcraft

Bracers (Leatherworkers only): Fur Lining - Stamina - Spell - World of Warcraft

Gloves (Engineers only): Reticulated Armor Webbing

Pants (leahterworkes only): Jormungar Leg Reinforcements - Spell - World of Warcraft (the exact same but a lot cheaper to make)

Rings (enchanters only): Enchant Ring - Stamina - Spell - World of Warcraft

Cat

Shoulder (inscribers only): Master's Inscription of the Axe - Spell - World of Warcraft

Back (tailors only): Swordguard Embroidery - Spell - World of Warcraft (Calculated over time it is about 90 AP)

Bracers (Leatherworkers only): Fur Lining - Attack Power - Spell - World of Warcraft

Gloves (Engineers only): Hyperspeed Accelerators

Pants (leatherworkers only): Nerubian Leg Reinforcements - Spell - World of Warcraft

Rings (enchanters only): Enchant Ring - Assault - Spell - World of Warcraft

Note: There is "some" sort of belt enchant (not an enchant really, but still a valid item improvement). [Eternal Belt Buckle] which a BS can make. It allows anyone to socket any (non meta) gem in their belt. No strings attacked. A BS can also socket their own gloves Socket Gloves - Spell - World of Warcraft) and bracer (Socket Bracer - Spell - World of Warcraft).

Personally i would never tank in TBC without [Formula: Enchant Boots - Boar's Speed] on my boots, and im using it on my current boots in wotlk.

As soon as i get my [Footwraps of Vile Deceit] i will be sticking [Formula: Enchant Boots - Tuskarr's Vitality] on them. I think for the small Stamina loss the added speed increase is more than worth the loss.

Other than that the list seems pretty solid, however [Fortitude of the Scourge] is no longer availiable, so we are stuck choosing between a warrior/pally or dps shoulder enchant for tanking. In my opinion until you have exalted with Son's of Hodir the dps enchant is a better option, but its just personal preference really.

Should Accuracy be considered in the Tank enchants for weapons? Formula: Enchant Weapon - Accuracy - Item - World of Warcraft

[Heavy Borean Armor Kit] seems like a better option then the honored one also.

Far as I know, it shouldn't.

The aura explicitely states other movement increasing effects don't stack with it. There's no movement increasing effects in general that do stack (other than PvP gear + Feral Swiftness).

I did not put Berserker up there because it is a very risky enchant. The AP gained is overall better then the steady 110, but it does remove 25% of your armor. In case of a not perfectly executed boss encounter you might get a hit and die. Also you might wanna switch form and tank a bit when the fight calls for it. If you forget to equip your tanking weapon or are not fast enough you die. You can use it but be sure when to use it. If you got 2 identical dps weapons... g4et one with this enchant sure!

True about [Fortitude of the Scourge]. Removed it.

Added the speed boots enchant. Speed is indeed very good in some cases.

Accuracy is not a bad enchant. But I would really not call it a tanking enchant. Crit is wasted and you don't really need the hit as tank that hard. You usually do more threat then any dps class does.
You could use it as dps, however it is really up to what you need. Though I thing you do more dps enchanting 110 AP then get a bit of crit and hit.

Good list. Was looking for something like this to bookmark since the Cat Megathread is showing its age with inaccurate enchant choices

Ok i"ll put it up because you insist. I'll add an asterisk to warn people about the drawback.

The link for fortitude on bracers is currently incorrect. It should be Enchant Bracer - Fortitude - Spell - World of Warcraft (or [Scroll of Enchant Bracer - Fortitude] if you want the link to the scroll)

Also, a viable alternative would be Enchant Bracers - Expertise - Spell - World of Warcraft/ [Scroll of Enchant Bracer - Expertise]

Changed thanks
And indeed, i had my doubts about expertise, but to avoid parry it is a very good stat!

Then also +20 hit on gloves should be added to the DPS gear list. It may not provide the highest crit or AP for the enchant slot, but you can be sure that hit rating will increase your dps until your capped.