Mixing Worlds
When doing some research to solve a geocache recently, I discovered the works of Aram Bartholl.
Bartholl is a Berlin artist who plays with the intersections of real and virtual life. His projects are really cool. Let me give you a few examples.
In his 2006 project "Map", Aram Bartholl recreated one of the well known location pins from Google Maps in the real world. The construction made from wood and cloth is the same size as a pin would be in Google's maximum zoom level.
In "Speed" he placed the neon light arrows marking the track in Need for Speed Underground into the real city of Bremen.
"First Person Shooter" took the idea to bring computer games into the real world even a step further.
He created glasses which add a Counterstrike weapon into your view field. Now hardcore gamers finally don't need to leave their known environment when dealing with the real world 
. You can even download a PDF cut-out sheet to make your own.
If you liked those, check Aram Bartholl's website for more pictures and videos.
Do you know of any other artists working on similar topics? Let me know.