You know the drill by now:
Astral Slide: Every block there are always multiple enchantments that play into whatever that block's key mechanic is. Usually these enchantments are just awful, like Rumbling Aftershocks, but Astral Slide broke the mold. Astral Slide is amazing because it plays defense very well (Cycling is instant speed and uncounterable after all) and allows you to abuse coming into play effects. Also, you can save your creatures from your own mass removal. It should be pretty clear why I would like a card like this by now.
Land Tax: White so rarely gets cards that generate obscene amounts of card advantage, nor does it get mana ramp very often. Land Tax does both of those things ... and for one mana. Some people might look at this card and think that that its mediocre since you can only get lands and you have to work to get it to activate consistently. However, people tend to underestimate how important thinning out the lands in your deck is. Since White doesn't have any card draw, in the late game you need to insure that you can draw gas, and Land Tax lets you do that. Also, it combos with Scroll Rack.
Limited Resources: Imagine playing this card turn one in a 6 player game. LOLOLOLOLOLOLOLOLOLOL. This card is banned in EDH :(
Mind Over Matter: This is probably one of the most degenerate combo enabling enchantments of all time. Seriously, the possibilities with this card are endless. Here are a few examples: Combine Mind over Matter with a land that produces a lot of mana on its own (Tolarian Academy) and a way to draw cards (Stoke of Genius). Combine Mind Over Matter with Niv Mizzet to deal damage equal to the amount of cards in your library. Combine Mind Over Matter with Temple Bell and an Eldrazi Legend to deck all opponents. The list goes on.
Necropotence: While the card seems confusing, it basically reads: "Pay 1 Life: Draw a Card". I shouldn't have to tell you how good this is and I'm surprised that this is even legal in EDH (but Bargain is banned go figure).
Oath of Druids: Basically, when you play Oath of Druids, you play it in a deck that only has like 1-2 creatures in it. As soon as your opponent plays their first creature, you get to reveal cards from your library until you get one of your 2 giant creatures. Or you can Forbidden Orchard to forcibly give your opponent a creature to activate your Oath. Alternatively, you could just run zero creatures in your deck, and just use Oath to dump your entirely library into your graveyard for some shenanigans.
Opalescence: Probably one of the more hilarious enchantments of all time. Opalescence actually is a very nice finisher for enchantress decks, especially after casting Replenish. But seriously, how does this card make any sense flavor wise?
Rancor: Still the best aura of all time and the only one ever worth running. Not only does it have an excellent cost to power ratio, but it also gets around the main weakness of auras: If your opponent kills the creature enchanted with Rancor, you don't get 2 for 1'd.
Recurring Nightmare: Despite being a stellar creature reanimator, Recurring Nightmare has a tendency to open up infinite combos. Example: Jet Medallion, 2x Priest of Gix (one in play the other in the graveyard), and Recurring Nightmare. That combo was a Zach favorite.
Sneak Attack: Sneak Attack was one of my favorite cards for a long time. Just imagine sneaking in an Emrakul or Blightsteel Colossus. Its also a lot of fun with Greater Good.
Story Circle: One of the problems with the original Circles of Protection, is that while they were really powerful, they were sometimes just dead cards. Story Circle circumvents that restriction, making it one of the best White defensive enchantments of all time. Seriously, play a Story Circle naming red against a red deck. There is literally nothing they can do.
Survival of the Fittest: A creature tutor and graveyard dump together in one neat hard to kill enchantment that can be activated multiple times. This card recently had to be banned from Legacy due to its ridiculous interactions with Vengevine. Even before that card was printed, Survival was a combo machine, especially when paired with Recurring Nightmare.
I just want to point out that a good chunk of these cards were from the Exodus expansion. Damn that set was so good. Anyways, my favorite of these is probably Mind Over Matter (although its a tough choice as Astral Slide and Sneak Attack are so good). Next up: Lands (this is the last card type to go over).