Thomas's Forgotten Realms
Being a trade city, Waterdeep honors all coinage, trade bars and electrum from throughout the Realms, as well as gems (which are traded as currency, rather than simple art objects, due to generations of dwarven influence).
The city mints its own coinage. 1pp (called a "sun") is equal to 10 gold (called "dragons") or 20 electrum (called "sambars") or 100 silver (called "shards") or 1000 copper (called "nibs")
Waterdeep also mints special coins: the square brass "taol" is worth 2 dragons, but has no value elsewhere, so they are usually exchanged when leaving the city; Palm-sized crescent-shaped platinum "harbor moons" are inset with electrum and rated at 50 dragons in the city (30 dragons anywhere else). Waterdeep coins have holes in them to allow them to be stacked in strings.