Are you playing a local executable (as opposed to playing on angband.live)? If so, you already have a list!
In the directory for your game, go here:
<Your angband directory>\lib\gamedata
Here, you'll see
monster.txt . Search through for the "unique" flag/bit of text.
Here's an example of what you'll find, searching for "unique" (notice the
flags:UNIQUE | MALE | POWERFUL in there)
Code:
name:The Balrog of Moria
base:major demon
color:v
speed:130
hit-points:3000
light:2
hearing:20
armor-class:150
sleepiness:20
depth:50
rarity:3
experience:30000
blow:HIT:FIRE:6d12
blow:HIT:FIRE:6d12
blow:CRUSH:HURT:5d12
blow:TOUCH:DRAIN_CHARGES
flags:UNIQUE | MALE | POWERFUL
flags:DROP_4 | DROP_GOOD
... etc etc etc