WhiningDog.net has a good review up of the Samsung YH-999 Portable Media Center. I looked at one of these at Best Buy and I fell in love. I'll probably pick one up soon. Read the full review here:
Review of the Samsung YH-999 Portable Media Center
...From the MCE operating system to the Windows Media Center Extender products, it's been clear that Microsoft's vision for digital media is finally starting to mature. With the MCE OS, consumers can tap into existing digital media from various sources and use it to their hearts content. With the Media Center Extender, users can now take this media (most of it at least), and distribute it around the house using a network. Completing the grand digital media vision is the Microsoft Portable Media Center which allows you to take the various media files that you may have on the road with you.