An online option for tracking art and artists is artprice (http://web.artprice.com/).

Artprice just opened as a global auction site in January 2012. There are free and paid memberships. If you're a paid subsciber then the benefits expand. But as a free subscriber, you can view starting bids on auctions, keep an inventory of your favorite artists, track their value, and place items for sale or auction. Artprice does take a commission ranging from 5-9% on auction sales. No charge on ads.

This is worth checking out as it's a very active marketplace. It claims 1,300,000 members.