Collection / Way of the Horse
Found this in a game, but is way better with trashing or strong engine pieces. It can even create a golden deck. As long as you can draw your hand and have 3-5 Collections, you can do the following:
1.) Draw your hand
2.) Buy 2-5 cheap action cards ($2-$3) with Collection's buy and payload, gaining between 6-25 VP with it
3.) Use Way of the Horse to return them to the supply, while also helping you draw your entire hand
4.) Repeat
This is especially good with Chapel. Chapel, as one of not the best trasher, is fast enough to give you a hand of 4 Collections and a Silver pretty early into the game, where you can then buy 5 Chapels for 20 VP each turn. Since Way of the Horse returns cards to the Supply on your turn, people can't counter this by buying all the Chapels after you set up.