Android: Plex is a great media center, and has a really convenient iOS app. Now that same app, minus the remote control (for now), is available for browsing and viewing your media center content on your much smaller screen.
Remote control function is coming soon, Plex promises, but in the meantime, you can peruse your auto-managed library and stream media to your Android. The streaming requires a bit of routing setup, similar to hooking up iOS and your computer through Plex.
Plex for Android is a free app. The developers note it's not tablet optimized, and also might not work on every Android device.
Plex for Android [Android Market via @nathos]