/r/specart has a lot of good stuff.

/r/imaginarylandscapes (and their sibling subreddits) is really high quality.

/r/earthporn if you like nature photography.

    /r/museum  
    /r/contemporaryart  
    /r/BackgroundArt  
    /r/ArtsHub  
    /r/artsphere  
    /r/CulinaryPlating (for chefs, but some of their creations are quite artistic)