Listing both Ancient and NE/Cenarion buildings here:
Ancients
Ancient of the Arcane
Seen in WoW, large Ancients with glowing crystals protruding from their bodies. Resembles a corrupted Ancient of War, but are actually buddy of yours. Can be easily created, I guess.
Could be useful for a Highborne race.
Ancient of the Wisp/Forest
A lumbermill-type Ancient building. Shorter and more bulky than most ancients, it has numerous small wisps going in circles around it, just like night flies around a lamp.
Ancient of the Oak/Wolf
Howling-Oak inspired ancient for Worgen sentinel units. Because, after the events of Cataclysm, it makes much more sense for Worgen to be used as NE units than as Human.
Tall, crooked, and leafless. Imagine Whomping Willow from Harry Potter. More of a black bark / crimson grass/remaining leaves
Ancient of the Spore
That's a bit too wild of an idea, I confess. An Ancient infested with Zangarmarsh shrooms.
Any Ancient winter/fall/spring variation
Buildings
Temple of the Moon (also here, here.)
Bulky rotunda with an open roof and a fountain inside. Acts as the spellcaster barracks for non-druidic sentinels.
Night Elven Farm
Come on, it shouldn't be THAT hard. Also, Night Elves built SUCH BEAUTIFUL gazebos (e.g. Lor'danel), that it's a shame that we don't see them here.
Lodge/Barrow/Homely House
Non-ancient Town Hall buildings. We have a helluva Night Elf lodges in WoW that can be used for inspiration. Shit, we even have
those fancy pagodas.
Tauren Totem NE style
For us, fans of the Cenarion Circle. A quick edit of the Chimera Roost would do.
Any. Highborne. Bulding.
Those are my two cents. They aren't even covering half of the possibilities. Problem with night elven architecture is that is too generic at times, and they actually prefer to live in ruins (damned hippies). Good thing is - it is so generic, that it has a lot of room for interpretation.