John Singer Sargent is one of my favorite artists and his Nonchaloir (Repose) c. 1911 is one of my favorite paintings. It's absolutely effortless and the colors are amazing. I love the large brush strokes and resulting loss of detail in the elaborate woodwork, embroidery, and furniture.
While in the National Gallery of Art I accidentally stumbled upon this painting. I've always loved it, and wasn't expecting to see it there. That's one of the greatest feelings... accidentally discovering a work of art you've loved and unexpectedly getting to see it in person.