I love the gameplay value that Grand Market's "no Copper" clause adds, so I thought of a few more cards along those lines:
Black Lab
$5 - Action
+1 Card, +1 Action. Gain the top card of the Black Market deck and put it in your hand.
You may not buy this if you have any treasures in play other than Silver.
Grand Herbalist
$3 - Action
+1 Buy, +$2. When you discard this from play, you may put one of your Treasures from play on top of your deck.
You may not buy this if you have more than one card of the same cost in play.
Mount Bank
$8 - Treasure/Attack
Each other player reveals their hands. +$ equal to the number of Treasure cards revealed. Then each player gains a Curse and a Copper.
You may only buy this if you have at least three Pearl Divers (from Dominion: Seaside) in play.
Peddlest
$5 - Action
If the cost of Peddler is exactly $5 when you play this, gain all of the remaining Peddler cards.
You may only buy this if the cost of Peddler is exactly $3.
Queen's Court
$7 - Action
You may choose an action card from your hand. Play it, oh, two times. No wait, four. I've changed my mind again. Three times. Maybe three and a half.
You may only buy this with a credit card.
Master Stash
$6 - Treasure
$2. When you shuffle, you may put this card anywhere in your deck, in someone else's deck, in someone else's hand, in any supply pile, or the box.
You may not buy this unless the number of cards on your Pirate Ship mat is equal to the number of coins on the Trade Route mat.