I count 16 $2 cards.
My ranking
Chapel - On most boards a must buy to get rid of your start cards fast
Courtyard - The best "deck-thinner" for its price. And if you draw a dead action card, just put it back. Great. Also mostly a must-buy.
Hamlet - one of the best villages available, and you can even have a +buy
Cellar - Maybe it shouldn't be so high, but I mostly buy 1-2, if there are no other "deck-thinner" available.
Crossroads - It's great to have at least one on boards with many good terminals to use +3 Actions, and it's great in the end to draw new cards for going green, so on most games it's useful.
Haven - It's great for equalizing draw luck.
Pawn - Similar to Hamlet, but benefit isn't that great. At least it can be a non-terminal copper.
Fool's Gold - Either it's so good, or so bad. So I leave it in the middle. You have really to know what you're doing if you buy this.
Lighthouse - Comparable to Pawn, but not that flexible. Of course great in 3+player games.
Moat - +2 cards is not that great, but on boards with a lot of attacks, especially in 3+games, it's one of the most important cards. You block 3 curses and draw your silver to get your Province. I can't understand all the haters. Yes, mostly there are better counters to Attacks, but not everybody plays only 2-player games.
Embargo - If you have the rare case that your opponent has a different strategy and you know it early on, then it's great. But mostly a one-shot silver if you don't have the luck to get to $3.
Native Village - This is also very board-dependant. The biggest problem is that you need a Spy or draw your whole deck and discard a card to know what you draw on your mat. On most boards this isn't possible. So you only get your +2 Actions.
Herbalist - I agree, that's not a great card. But it's useful like Scheme is useful. Just put your Potion or Gold back on the deck. It can guarantee a next turn Province buy.
Secret Chamber - I don't like it. It's a bad Vault and heavily depends on the Attacks in the supply. I think it's worse than Moat.
Pearl Diver - It doesn't hurt, but the benefit is minmal
Duchess - The uses are rare, e.g. a VP rush with Duchies and Dukes, all other times it's useless.
Edit: Forgot Embargo