Alright - back again. Since sea levels were all within thousandths of a game yard from one another, I just went with absolute heights.
Nordrassil (the World Tree) is the clear winner here, as it should be. The upper leaves reach a point of 2,713.4 game yards above sea level, and the highest part you can actually stand on, is still higher than any other location, at 2,450.7 GY
As for the rest - a combination of tall points, and guesses from this thread:
3. The tips of the spires of ICC, Icecrown (2,153.9)
4. Temple of Storms, Storm Peaks (1,990.4)
5. Unnamed Hyjal peak {67.67, 37.60} (1,970.6)
6. Unnamed Hyjal peak {53.50, 39.60} (1,889.4)
7. Temple of Storms, Storm Peaks (natural geography) (1,880.5)
8. Ulduar's roof, Storm Peaks (1870.7)
9. Temple of Order, Storm Peaks (1832)
10. Terrace of the Makers, Storm Peaks (natural geography) (1665.3)
11. Highmountain Peak, Highmountain (1577.9)
12. ICC, Icecrown (Lich King Platform) (1544.1)
13. Violet Citadel tip, Dalaran (Broken Isles) (1279.3)
14. Neverest Pinnacle, Kun Lai Summit (1229.5)
15. Violet Citadel tip, Dalaran (Northrend) (1191.9)
16. Shala'drassil, Val'sharah (1179.1)
17. Veiled Stair peak, Pandaria (1137)
18. Reflection Peak, Highmountain (1125.2)
19. unnamed Kun-Lai peak {54.01,54.08} (1000)
20. Kota Peak, Kun-Lai Summit (920.921)
21. Unnamed Dun Morogh peak {64.11,26.13} (896.3)
22. Heart of Fear (891.2)
23. Twilight Citadel (879.7)
24. Blackrock Mountain (858.5)
...
??. Wyrmrest Temple (441.7)