This is a list of cards that do things no other card in the game does (which obviously depends a bit on your interpretation of "things no other card in the game does" so you might have some disagreements):
Base:
Bureaucrat and Library
Intrigue:
Masquerade, Conspirator, Minion, Lurker, Courtier
Seaside:
Embargo, Ambassador, Smugglers, Outpost, Treasury
Alchemy:
Scrying Pool, Possession
Prosperity:
Watchtower, Mint, Vault, Bank, Forge, Peddler
Cornucopia:
Young Witch, Tournament
Hinterlands:
Duchess, Develop, Tunnel, Noble Brigand, Nomad Camp, Inn, Mandarin, Margrave
Dark Ages:
Poor House, Squire, Fortress, Knights, Pillage
Guilds:
Doctor, Butcher, Journeyman
Adventures:
Caravan Guard, Messenger, Haunted Woods, Storyteller, Wine Merchant
Empires:
Royal Blacksmith, Castles, Chariot Race, Enchantress, Fortune, Villa, Capital, Crown
Nocturne:
Druid, Faithful Hound, Pixie, Changeling, Necromancer, Werewolf
Promos:
Black Market, Stash
It's also a pretty decent checklist for "Easy Puzzles" solutions.