Here are some sites I have found inspirational, and which are worth your time.

1.
You've heard of Steampunk? Well, Dieselpunk is sort of the same deal, only glorifying the uh... gloriousness that is early 20th century modernism.

2.
You know what this is? It's the Google Art Project. And it's brilliant. Thousands of hi-resolution images of artwork from around the world, taking in hundreds of art collections. You can zoom WAY in close to works of art and see the very brush strokes of the masters. It is the best time-sink on the internet. Go there. Go there now.

3.
For years now, I've followed the good people at Lines and Colors. One of the best jumping off points to artwork out there.

4.
Retronaut. What are you waiting for? 

5.
I've got a wicked love of bleakness and nihilism. Here's a fun little site that scratches that itch: End of Being.
More to come later. Follow the links.