Sabers and hippogryphs are the best night elf mounts imo, but if you want something a little different you could also use the Ashenvale Chimaera from Darkshore.
As for tmog, there’s several different routes you could take… sentinal, warden, druid/naturey, etc… My night elf rogue has a warden-esque look, though I prefer to use the Priestess’ Moonsaber that others have already mentioned
On that we agree… but out of the original cat mounts I think it is still the best looking. A model refresh, ie making a high res version of the original model would be cool.
Warfront armor and nightsabers if you want racial pride.
Racial pride as a night elf 
Ishnu’alah Sneakybebe!
Below are some ideas, if you’re looking specifically for Darnassian (night elf) themed items and sets. If this particular theme is not what you’re interested in, my recommendation would be to browse wowhead.com to find the aesthetics you’re looking for for your character.
https://www.wowhead.com/item=68824/swift-zulian-panther
https://www.wowhead.com/item=166435/kaldorei-nightsaber
https://www.wowhead.com/item=166428/blackpaw
https://www.wowhead.com/item=143764/leywoven-flying-carpet
https://www.wowhead.com/item=69213/flameward-hippogryph
https://www.wowhead.com/item=141217/reins-of-the-leyfeather-hippogryph
https://www.wowhead.com/item=45725/argent-hippogryph
https://www.wowhead.com/item=29471/reins-of-the-black-war-tiger
https://www.wowhead.com/item=46813/silver-covenant-hippogryph
https://www.wowhead.com/item=45591/darnassian-nightsaber
Wait, how is the Enchanted Fey Dragon and Raven Lord a Nelf mount? They’re not even from Azeroth… they’re from Draenor.
It’s more aesthetic than literal. Night/Moon themes, also faerie dragons are WCIII units and a lot of night elf players do enjoy the faerie dragon mount for that reason.
Oh, that looks… What is that work I am looking for?
I don’t know but man those boots look terrible. They’re so… big.
Yeah, the boots does look extremely big. But you also have Paladin sets where the boots are quite big too.
You can get the updated Hippogryph from the quest where Teldrassil is burned. That said, if your mog is not purpleish, it might clash with it, but not too much.
It also depends if you want a casual Rogue one, or a Blizzard Rogue style where the armor looks a bit too big for a class supposed to stealth it’s way to battle.
I can’t describe how happy this list has made me. Thank you so much! Lots of excellent content to work towards and, along with the other contributions, it was exactly what I was looking for.
This forum has been so helpful I’m actually floored.
Glad I could help. Happy hunting! 
Why no shoulders on the darkshore one? It seems so odd. Like her lower body is protected like crazy with those boots, but the upper body is just open.
It could work with either smaller boots or adding shoulders.
I’m not sure, that’s how that trasmog designer chose to design it. 
As with all things, they are optional.
Ohh i thought that was a designed by you kinda thing.
I would spare the OP that. I’m partial to Classic transmogs, which is not among the most popular picks. LOL 
Though, I could try my hand at a few Darnassian ninja type mogs. I’m not well-versed in Leather mog options, being a hunter main.
Big is beautiful 
Also great for walking over my victims 
In before someone says a bikini and a tiger mount?
I think something fiery…too soon?
