John Everett Millais' 'Ophelia' is currently on display at the Van Gogh Museum. Based on the scene in 'Hamlet' of Ophelia drowning (which Shakespeare left open for interpretation as an accident or suicide), the painting depicts the moment just before her death, when she floats down the river singing.
...Her clothes spread wide,
And, mermaid-like, awhile they bore her up;
Which time she chanted snatches of old tunes,
As one incapable of her own distress,
Or like a creature native and indu'd
Unto that element...
(See here for the rest of the passage.)
A founder of the Pre-Raphaelites, Millais infused his paintings with an intense love of nature in all its luscious detail, and he had a great eye for dramatic moments. In a time when photography was being invented, Millais sought images that would do more than just capture reality; they would have to tell a story. (Many of his paintings are based on stories or poems, notably by Tennyson.)
With these aims, Millais created some very powerful and 'telling' portraits, especially of women, as well as some beautiful, expressive landscapes. Yet it's easy to see why 'Ophelia' is his most famous work, as it seems somehow to combine the best elements of all his other work.
The Tate Britain website has an in-depth section on the painting's history and symbolism. (Yes, every single flower has symbolic meaning; e.g. orchids as "dead men's fingers".)