The Enigma Order

There are 25 guild levels and each level will automatically reward with an extra perk. The leveling process remains unchanged and your guild will gain experience through PvP, Dungeon and Raid progression, questing, etc ...

Guild currency has also been removed and rewards will just be "unlocked" after you reach a specific level or complete a guild achievement. Once a reward is unlocked, members will be able to purchase it with gold. Some of the rewards include guild tabards, mounts, heirlooms, and it looks like you will finally be able to have a guild tabard on your mount. (Just like the Argent Tournament banners)

New members of a guild won't be able to buy everything directly, they will have to contribute to the progression of the guild before they can access the top rewards. Each time a player helps towards the leveling he will gain reputation with the guild, the best rewards will require players to be exalted with their guild before they can buy it.

Level        Spell                                              Description
1         Fast Track (Rank 1)                Experience gained from killing monsters and completing quests increased by 5%.
2         Mount Up                               Increases speed while mounted by 5%. Not active in Battlegrounds or Arenas.
3         Mr. Popularity (Rank 1)           Reputation gained from killing monsters and completing quests increased by 5%.
4         Cash Flow (Rank 1)                Each time you loot money from an enemy, an extra 5% money is generated and deposited directly into your guild bank.
5         Fast Track (Rank 2)                Experience gained from killing monsters and completing quests increased by 10%.
6         Reinforce (Rank 1)                 Items take 5% less durability loss when you die.
7         Hasty Hearth                          Reduces the cooldown on your Hearthstone by 15 minutes.
8         Reinforce (Rank 2)                 Items take 10% less durability loss when you die.
9         Chug-A-Lug (Rank 1)              The duration of buffs from all guild cauldrons and feasts is increased by 50%.
10         Mobile Banking                       Summons your guild bank. Instant, 1 hr cooldown
11         Mr. Popularity (Rank 2)           Reputation gained from killing monsters and completing quests increased by 10%.
12         Honorable Mention (Rank 1)     Increases Honor points gained by 5%.
13         Working Overtime                  Increases the chance to gain a skill increase on tradeskills by 10%.
14         The Quick and the Dead          Increases health and mana gained when resurrected by a guild member by 50% and increases movement speed while dead by 100%. Does not function in combat or while in a Battleground or Arena.
15         Cash Flow (Rank 2)                Each time you loot money from an enemy, an extra 10% money is generated and deposited directly into your guild bank.
16         Guild Mail                               In-game mail sent between guild members now arrives instantly.
17         Everyone's A Hero (Rank 1)     Increases Heroism points gained by 5%.
18         Honorable Mention (Rank 2)     Increases Honor points gained by 10%.
19         Happy Hour                            Increases the number of flasks gained from using a flask cauldron by 100%.
20         Have Group, Will Travel          Summons all raid or party members to the caster's current location. Unlimited range, 6 sec cast / Channeled, 2 hr cooldown
21         Chug-A-Lug (Rank 2)              The duration of buffs from all guild cauldrons and feasts is increased by 100%.
22         Bountiful Bags                        Increases the quantity of materials gained from Mining, Skinning, Herbalism, and Disenchanting by 15%.
23         Bartering                               Reduces the price of items from all vendors by 5%.
24         Everyone's A Hero (Rank 2)     Increases Heroism points gained by 10%.
25         Mass Resurrection                  Brings all dead party and raid members back to life with 35 health and 35 mana. Cannot be cast when in combat. 64% of base mana, Unlimited range, 10 sec cast

No news about what you need to do to level up the guild and gain rep with it yet though.