The official Plex application has just been approved by Barnes and Noble to be listed in their app store. This gives the Nook Color and Nook Tablet the unique ability to access your computer or network and stream video to your device.
Plex is a great application that is much akin to other services on iOS and Android. In order for the process to work properly, you have to install some server software on your PC. Once you do this and purchase the app from the Barnes and Noble App Store ($4.99), you can begin to access movies and television shows that are stored on your PC. One of the boons of this software is that you can easily access your iTunes library and playlists.
The Nook line of Tablets tremendously benefits from this method of accessing your media, because the company limits the amount of content you can load in the main memory. Sadly, you are relegated to only 1 GB of data that you can copy to your Nook Color or Nook Tablet unless you use a MicroSD card. Accessing the data from your PC directly bypasses this restriction and allows you to play with more content than you would normally be able to load.