Good Android app for playing network media?

[Bryan Cahoon]

I'm just beginning to formulate this idea in my mind, so I don't know how doable it is with the android ecosystem. I am thinking of getting a "travel router" and putting it in my car, and putting some cheap tablets in as well (ie, with dash and head rest mounts) so that for long trips, there is something for passengers to do. I'd like to attach mass storage with music and movies, so that each person has a solid library to choose from - but I want to make it as beginner proof as possible so that my passengers don't have a steep learning curve. Is there a good app or suite of apps to do this with? I considered the possibility of a Plex server in the car but A) I'm not sure how much data a Plex server uses (all streaming would be local to the car) and B) it looks like I would need something other than an Android device to be the server.

I COULD just put an SD card in each tablet, but mass storage would definitely allow for a much larger library. Any suggestions? Or am I barking up the wrong tree trying to do this?