Let mw start by saying I know a ton of people disagree with Shaman tanks. Also that the likely hood that it ever happens is slim to none. Nonetheless, it is something I personally am intereasted in and have thought about for a long time. So I wasted some of my time and built a workable spec into the current Shaman scheme. It's not something I expect people to care about or agree with. It's just something that because of my intereast in , I felt like doing. It looks something like this:
Guardian Shaman
15 - Removed for movement tier. Astral Shift becomes baseline for all shaman specs ( equalizing Shaman with all other classes ). Stone Bullwork becomes a Guardian spell learned near 76 as a defensive cooldown.
15 - Planeshift - Shift through the Elemental Planes appearing 10 yards forward.
Riding the Wind - Inceases targets speed by 20% for 6 Seconds
Attunement - Your natural attunement with the Elements grants you a constant 15% to movement speed
30 - As is
45 - Personally think this is a wasted tier but no ideas how to replace it as of now.
60 - As is
75 - As is
90 - Elemental Blast = As is for Resto/Ele/Enh - New tooltip for Guardian reading Dodge, Parry, Block instead of Crit, Haste, Mastery.

Active Spells
Focus Fury - The Shaman makes himself the focus of all the targets Fury ( taunt )
Earthquake - While in guardian spec, Earthquake is instant cast on a 45 second cooldown and generates extra threat ( ie Concecrate/Death and Decay ) ( Can actually be used as is as well. )
Elemental Hammer - The Shaman fills his weapon with Elemental energy and slams his weapon down damaging all enemies within 8 yards and causes physical damage dealt from affected targets to be reduced by 10% for 25 seconds
EarthStrike - Takes the place of Primal Strike. Stikes the enemy with all the force of the Earth.
Frost Shock - As is. Added effect - Used to consume Flame Shield Orbs
Flame Strike - You super heat your weapon with fire and strike the target dealing X amount of damage.
Imbued Shield - Your shield is temporarily imbued with elemental force that you can use to slam into your target for additional damage
Totem of Renewing Energy - Earth - Because the Guardian is especially in-tune with the Earth he is able to constantly be renewed with it's energy restoring 2% mana every 5 seconds. Last for 1 minute. 30 yrd range

Fire Shield - Surrounds the Shaman with a fire orb that casts light on enemy attacks adding 1% to your block and parry and an additional 1% per charge. ( could also allow earth shield for Guardian instead )
Rockbiter Weapon - Increases threat and reduces damage taken by 10%

Defensive Cooldowns
Stone Bulwork - Becomes available in Guardian
Shamanistic Rage - Carries over from Enhancement
Astral Shift - Baseline for Shaman
Ascendance - Guardian - While in the form of an Earth Ascendant, Earth Spike becomes instant and you are shielded for 10% of each Spike cast for the duration.
Water of Life - A bubble of water surrounds the shaman increasing health by x% and increases healing taken by x% for 8 seconds
Vortex Totem - Summons a totem that lasts 3 seconds but absorbs all spell damage that would affect the raid for the duration into a vortex into the Elemental Planes
Link of Life - Due to the nature of the Shaman's spiritual attunement, he can temporarily link his health with another player and all damage taken will be split between them for the duration. Last 8 seconds
Passive Spells
Mail Specialization - Grants additional armor for Guardian
Mental Quickness - Carries over from Enhancement
Wayward Wind - Your attunement with the elements grants you extra reflexes increasing dodge by 5%
Maelstorm Weapon - Active as Guardian - Could be used for Healing Wave/Healing Surge or for extra dps from Chain Lightning ( A form of active midigation by self healing )
Earthen Defense - ( Passive ) Your attunement to the Earth grant you increased Stamina and Armor ( by amount equal to other tanks )
Growing Flame - Each Flame Strike cast has a 60% chance to generate an additional Fire Orb when Flame Shield is active up to a maximum of 7 ( like Elemental Rolling Thunder )
Fulmination - While in Guardian when you have more that 1 Fire Shield charge active your Frost Shock will consume any surplus charges. Casting Frost shock counteracts your Fire Shield supercooling the air around you and creating an barrier around the Shaman. X amount of damage is absorbed per charge. ( Second form of active midigation )
Glyph of Earthstrike - Your earthstrike damage can be split between up to two targets
Glyph of Fire Shield - Your Fire shield will always give an additional 1% to Parry and Block when active
Your critical strikes increase your chance to dodge by 5% for 5 seconds. Each point of Mastery increases dodge chance by an additional 5%

Basic Rotation
1. Apply Rockbiter for threat and damage reduction
2. Apply Fire Shield for additional defense and for Growing Flame stacks
3. Place Totem of Renewing Energy - Maintains mana to cast spells - Maintain Uptime
4. Earthquake - Establish threat/Aoe
5. Elemental Hammer - Applies Weakened Blows/Aoe
6. Elemental Blast/Unleashed Fury pending on choice for damage reduction - Use on CD
7. Place Searing or Magma Totem - If searing can be placed pre pull
8. Flameshock - Only if single target to increase damage
9. Earthstrike - Longest offensive CD spell. Most damage
10. Flame Strike - Works with Growing Flame/Fulmination - Best Filler
11. Imbued Shield - Filler
12. Frost Shock - Lose stacks of Parry/Dodge but gain Absorbtion
13. Maelstorm Weapon - use at 5 to cast Healing Wave/Healing Surge for self preservation or to cast LB CL for extra damage if preservation isnt necessary.

-Shamans already use shields and currently have Rockbiter weapon. They have several spells that transition over well and also have a setup that would make a tank transition easy. And this setup can be tweaked a bit as needed. For instance Totem or renewing energy can be removed and a mana return added to Flame Strike instead. Several other tweaks would be easy to make. But this is how easy a tank transition for Shaman would be. Of course the numbers for the spells would need major refinement and I'm not going to waste my time even making relative values for the spells simply because this will never come to light and there is no point. But I would like some feed back on what otehr shaman think about something like this.