ADOMs itemset:
[ Armor, shields, cloaks, boots, girdles, gauntlets and helmets
* Gems and rocks
] Tools (keys, writing sets, elemental orbs, and various other things)
' Necklaces
( Melee weapons (all of them)
} Missile weapons (bows, crossbows, slings)
/ Missiles (arrows, quarrels, etc)
= Rings
\ Wands
! Potions
? Scrolls
~ Bracers
% Food (inc corpses and herbs)
$ Gold
{ Musical Instruments
" Books
Most items have certain colour sets to represent certain types (wooden weapons are brown for instance), whilst artifacts tend to be particularly identifiable based on their colour.
Monsters are almost all represented by upper or lower case letters. Important NPCs (including shopkeepers) tend to be @, whilst demons are usually &. The letter/monster grouping is a bit odd but functional - various races are generally grouped into a letter type, with colour distinguishing between individual types. For instance many small humanoids are h, whilst giants are H. Lesser undead are z, and more powerful undead Z.
Terrain is mostly . and # with different colours for terrain type. Also used are T for trees and = for water. The world map also uses various symbols like ^ for mountains and ~ for hills.
There's various faults I'd raise with it too (like arrows and open doors looking the same), but it's mostly very functional, and importantly I think the aesthetics of the colour and symbol choices work very well.