Undead Leveling 1-50

[Aerar]

Kith at night is a suicide mission and should be both feared and respected

[hillgiantchamp]

Spectres in oasis, oot, feerott great for 35-45

[Malone88]

Plenty of skellies in Lake of Ill Omen by the ruins/windmill -- XP off
them from 25-35ish. Also remote chance to kill Sarnak Courier who
ultra rarely drops a 9k item (Goblin Gazughi Ring).

[Yumyums Inmahtumtums]

1-9 - anywhere.
9-16 - Najena, Befallen, Kurns Tower, Unrest, WK skele ruins
16-24 - Kurns, Unrest, Paineel, Rathe Mountains, Butcherblock
24-34 - Unrest, LoIO, Rathe Mountains
35-44 - Unrest, Rathe Mountains, Feerrott, Oasis, Dreadlands, CoM, EJ, Kaesora
44-52 - Dreadlands, Oasis, Feerrott, CoM, EJ, Kaesora, TT, KC, BW

Some zones are listed multiple times but that's just to show range. There's prolly more but going off memory.