Old Witch: her magic isn't as powerful anymore but she is more experienced and knows how to do more things.
Bureaucrat: delaying your deck with useless cards. Just what bureaucracy does!
Pirate Ship: send your ship on a raid, see what it brings back.
Grand Market: this place has the best products, but they won't even let you enter if you are a poor fellow who carries coppers.
Watchtower: watches and fires arrows at anything that tries to invade your kingdom.
Menagarie: the more different animals you have, the more people will come.
Cultist: joining a cult will ruin all your finances, and make you act as a mob to ruin other places.
Advisor: he has all the advices you need, but he will take the best ones for his own gain.
Bridge Troll: not as beautiful as the Bridge or fast like the Highway, but this bridge has a troll that will attack your enemies if they try to pass it.
Page: how a farmer got recruited, realized that war sucked, became a fugitive, then hid in a monastery but eventually became its master.
Fountain: throw a copper and something good will happen. Throw 10, and something great will!
Tragic Hero: he will fight for you, but make him fight too much and he will die tragically to give you a final gold.
Recruiter: someone needs to make your Pearl Divers and Vagrants join the army to become real men.
Fleet: you don't know if it will accomplish anything, but you send it. But one day, they will come back having colonized a few extra duchies.
I love internal game flavor that doesn't translate outside Dominion but has become engrained in our collective consciousness as reasonable nonetheless; e.g., the experience of being haunted is similar to putting things from your hand on top of your deck, or, locations where royalty are found allow you to repeat something you've already done.
Discard attacks are usually related to violence.
Cursing attacks are related to magic.
Trashing attacks are related to theft. Same for Spoils.
Trashing is related to religion, since you are donating your stuff.
Cards related to movement usually draw.