based on what 80's have said positive or negative and from players in the BGs
travelers tundra mount, do a wotlk 10 day trial. do the quests at amber ledge, and coldara for the rep. along with the daily cooking and fishing quests in dalaran. also turn in any waterlogged recipes, you get from fishing. you should be able to hit honored which makes mount 18000. many players will believe at 70 you paid the full 20000. have your fishing and cooking at 375 before doing trial. many 80's are happy when i have popped it in SWP, Kara, ZA, so they can vend etc.
BC netherdrakes, for some they either forgot or don't know where they are from. i have been in TK, BT, etc. raids with 80's and when i fly in on a netherdrake, many are amazed to see a 70 on one? also many don't know that after you get one free on the final quest to shat, you can go back and buy the other 5 colors
Halaa PVP mounts, get alot of questions when i'm on either one. many don't know about those 2 specific ones from halaa vendor
my 70 has over 50 mounts, and when on a albino drake, get a ton of Q's also
even if i pop a nether ray mount from skyguard, you realize from Q's. how many players are new to the game, and just ripped to 80.
ashes of alar would be cool, you will need a guild to run you for that, 80's fight and die over that mount
for horde i think a twink would be impressive on a zulian tiger
for alliance i like the winterspring frostsaber
you got $$$..... spectral tiger