The great resource that is known as Art.sy has just been made open to the public. Art.sy states:

We provide one of the largest collections of contemporary art available online. Thousands of works from all cultures and time periods are accessible for study and enjoyment, and select works from our gallery partners are available to collectors. By making all the world’s art freely accessible, Art.sy hopes to foster new generations of art lovers, museum goers, collectors, and patrons.

What I like about Art.sy is that it allows you to search by various subjects, movements and more (as pictured below). It can also make recommendations for you too. Start browsing!