I went to an exposition of J.W. Waterhouse once. I still have the poster of it. Yeah, that was great. I also love the other pre-Raphaelite brotherhood's stuff.
This, for instance, is Ophelia by Waterhouse.
This one is Odysseus by Waterhouse.
As for modern art, I see a lot of great art on Magic: the Gathering cards. Raymond Swanland's art is fantastic, for one.
The art below is not M:tG but a cover for a book, but point stands.
I've also met three artists in person, so I may be a little biased towards them. They are rk post, Mark Tedin, and Pete Venters.
The below is by rk post.
This one card art by Mark Tedin:
Pete Venters art is next:
I didn't get to meet her (the line was too long at another convention than frmo the one where I met post, Tedin, and Venters) but I also enjoy the art of Magali Villeneuve. This piece of art is almost too gorgeous to be put on a token (a card that can represent things that card effects put in the game). Then again, if you put the art on tokens, you see more of it.