This timeline is very incomplete, so feel free to send me your suggestions. I’ll be adding more entries on a regular basis.
1995-1998 - Allwall.com, AllPosters.com and Art.com each launch separate e-commerce sites to sell fine art prints and posters. They are the first websites (other than eBay, perhaps) to offer large volumes of decorative art for sale.
1999
August - CafePress.com opens its doors, making it easy for artists to put their artwork on apparel, mugs, mousepads, and more. . . all while listing it for sale in the CafePress marketplace.
December - ArtSpan.com launches as one of the first services to offer individual portfolio websites for artists.
2000
August - DeviantART.com appears on the scene, and slowly becomes the largest online art community in the world. (DeviantART now offers print-on-demand services for its artists as well.)
November - EBSQart.com begins with a simple mission—support living artists—and fulfills that mission by creating an online community with portfolio tools for artists.
2001
May - Allwall.com buys Art.com and consolidates their online presence under the Art.com website and brand.
July - Zazzle.com launches a competitive service to CafePress.com and gives artists another venue for selling their customized products and apparel.
August - FineArtStudioOnline.com launches it’s own personal art portfolio service for artists.
August - Google creates Image Search, giving artists and art buyers a whole new method to search for art and images online.
2002
September(?) - Yessy.com opens its online art gallery for artists.
2003
August - BoundlessGallery.com launches an online gallery for artists.
2004
February - Flickr.com gives photographers all over the world the opportunity to share, organize, and comment on photos.
July - Art.com starts offering original artwork for sale via its “Original Art & Photography” community.
December - Duane Keiser begins posting a new painting on his blog every day while selling many of them at auction on eBay. His success sparks the widely popular daily painting art movement.
2005
June - Etsy.com creates a community marketplace for hand-made items and artwork.
2006
March - AllPosters.com and Art.com merge into Art.com Inc. with both websites remaining active.
May - Saatchi Online launches and quickly creates a viral internet sensation with its Saatchi Gallery Showdown.
September - Imagekind.com creates a free print-on-demand service for artists.
November - EmptyEasel.com appears. :)
2007
February - RedBubble.com begins offering a free print-on-demand services to Australian artists.
February - Art.com Inc. launches Sistino.com (a print-on-demand marketplace for contemporary artists) and ArtistRising.com (a marketplace for original artwork).
July - RedBubble.com opens its doors to international artists.
November - Art.com Inc. closes Sistino.com and merges its print-on-demand services with ArtistRising.com.
2008
July - CafePress.com acquires Imagekind.com.
2009
February - Zibbet.com, another Australian company, opens its online art gallery.
April - Foliotwist.com (a company I co-founded) begins offering blog/portfolio websites for artists.
April - Zatista.com launches an online gallery for artists.
More to come soon. . .
Any suggestions or corrections? Notify me and I’ll add them to the timeline.