Actually I'm kind of surprised this isn't a more common fan art theme.
More cool horror themed art & tees available at the ZombieDollar Creative's RedBubble Store.
Including this excellent Word of Warcraft/Cthulhu parody! Via Shirtoid.
Actually the concept is pretty witty. The Neo-Preppy fashion brand's mens fall look book features Potter Alums Tom Felton and Rupert Grint hanging out at LA's Magic Castle in a series of old Poloroid styled photos. More photos @ 80's Purple and Highsnobiety
Andrew Williamson has done really beautiful concept art for the Potter Film Series - starting with Chamber of Secrets and running all the way through to The Deathly Hallows Finale. You can really see how his work set the mood for many key scenes. Much more art at his portfolio site.
Collider provides a brief video tour of the extensive collection of movie props and costumes on display at Harry Potter: The Exhibition at Discovery Times Square, New York. This looks like fantastic show for both Potter fans and those interested in film production design. It runs through September 5th, 2011.
Entertainment Weekly has a really great info hub - Harry Potter Central. Tons of behind the scenes photos, video clips, and the latest shots of the cast from the London Premier, with much more coverage to come.
Two cool features are excellent high res photo galleries of actual props and sets from the
films that you can examine up close with a magnifying glass.