Best way to stream movies from an external drive?

I'm a movie guy. I have a growing collection of my movies on an external drive connected to my MBP. Right now I use an Apple TV 3 to watch my movies in the living room. The rub continues to be that my computer needs to be on with iTunes running. That's kind of a pain, as is having to add movies to my iTunes library before the ATV will see them.

What I would like is to be able to plug my HDD into something (my Airport Extreme router or a box you recommend) and that will allow me to browse my movies and play them without needing my computer to be on. I believe the Boxee Box and one of the Roku's do this (2 XS). I'm not sure I like the WD Live + because it's tied to the hard drive — I may need to upgrade drives or move to NAS.

Outside of not needing my computer, my next request would be to have an pleasant easy-to-use UI. I like the Apple TV UI and I like the Plex UI on my Mac, too. Something like these will work fine.

Recommendations, up-and-coming products, alternative ideas? All are welcome.