The Google Art Project is a fantastic resource for artists, art lovers and teachers. It is born out of the collaboration between Google and 17 major art museums around the globe.
The site has several components. One is the ability to visit some rooms in each museum (Google used their Street View technology) where you can go around and look at the paintings.
As an artist, the most interesting feature is the super high resolution photographs of artworks. Each museum selected one painting. You can zoom on the painting down to individual strokes. I recommend that you look at the selection from the Van Gogh Museum in Amsterdam as it shows very well the artist’s vigourous brush strokes.
You can read Google's press release for more details.