The first really great Impressionist painter, in my opinion (And from here out it's all my opinion!) was Claude Monet. Before him, painting was done in the slick and tight Classical style. Those paintings didn't suck, but Monet and a few others thought that they didn't depict Nature accurately. So they dragged their easels outside, and painted what they saw. It wasn't too long before that whole style came across the Atlantic Ocean to America, where American artists embraced it. Here's my favorite practitioners of Impressionism. Not a paint slapper among them! They broke down Nature's colors, and reassembled them in a fresh way.
In no particular order, let's start with William Merritt Chase.
This one is a pastel, and what a great job he did! That gray is really the paper. But his style epitomized Impressionism: Broken bits of color our eyes assemble to make a coherent whole. He didn't scribble one shade of green, he broke it up with blues and purples, yellows and reds separately.
Here's another great, if somewhat under appreciated painter, Willard Metcalf.
Metcalf painted in New England primarily. When I see a Metcalf, I think I'm home. No comfy studio for Will, this guy was an outdoor painter all the way. In my forays outside to paint, I try to channel his spirit to flow through me. Apparently my psychic skills are as bad as my plein air skills. Now, here's a Frank Benson:
Frank posed his daughters and their friends for this one. He did paint outdoors, but wasn't against finishing things up later in the studio. But Benson was a genius at depicting bright sunshine. I don't think you could pull this off solely outside.
The painting above is by a true plein aire painter by the name of Daniel Garber. He did his thing around eastern Pennsylvania. I love everything I've seen of this guy. This is how a plein aire can really look. It's honest, it has great atmosphere, and it is as far from slap-dash as Catherine Zeta-Jones is from ugly!
Another American painter, but I'm sure he spoke with a decided French accent from spending almost his whole life in Europe was John Singer Sargent.
If Sargent had never existed, we'd probably know this next guy better:
Anders Zorn. Zorn and Sargent are the Patron Saints of the current American Realism movement. You can see their influence in artists from Jeremy Lipking to Richard Schmid.
One last great American Impressionist before I go. I don't know about you, but I think he was the best one of them all: