Ilya Tyljakov really beautiful atmospheric landscapes and concept art, using his specially modified brushes.
It is possible to create really beautiful watercolour and painting effects using modified brushes. Below are what I found to be the most atmospheric and innovative.
Realistic painting tends to use the round brush and/or airbrush, building things up slowly with transparency to create very photorealistic effects.
Below: The subject matter is pretty cliche. But interesting use of underlying tonal drawing, then overlaying colour with blend modes.
Drawing and inking
Architectural illustration from a photo
Manga and cartooning
These all tend to use a similar soft fantasy style
Stefan de Groot Dutch illustrator produces a lot of good tutorials, particularly on basic illustration and realistic painting, though I do not find his work as atmospheric and innovative.
James Julier realistic pencil sketches, fantasy art and landscape
Danny Glasgow landscape and fantasy
Austin Bachelor colours over line art.