It is difficult to make this a short list as there have been many great artists, both past and present, whose work is very inspirational. Rembrandt, Raphael, Michelangelo, Bonnington, Turner, and the work of the Newlyn School.
I have always admired the Watercolours of Edward Seago, Jack Merriott, Trevor Chamberlain, David Curtis, Authur Melville, Charles Reid, and Sir William Russell Flint. The latter's absolute mastery of this difficult medium is something I find particularly impressive.
I also find a particular affinity with G John Blockley whose inspirational paintings have influenced many artists since. I love the colourful Pastels of Norman Smith and modern Plein Air painters like Richard Schmid and Kevin Macpherson. I also admire the work of David Leffel and Robert Lenkiewicz. For me painting is all about the transforming effect of light. This can be very simple as in the work of John Miller or something more laid in as in the work of Neil Pinkett. I also admire the work of the old school RA's:- Colin Hayes, Fred Cumming, Ken Howard, Bernard Dunstan and Diana Armfield.