After a year with the AppleTV I decided it was time to do something about the only deficiency it had: The inability to play x264 encoded files.
Following advise from some of my fellow nerds I ended up bying a Tvix HD M-6500A.
The box itself is solid and even if some might find it less aesthetically pleasing than the AppleTV I think if looks good.
Versus

This is, in my opinion, how the Tvix stacks up against the AppleTV
Pros
- Most importanly it supports true HD content including x264 encoded
video in Matroska containers - Support for a wide range of files (None Quicktime movies requires hacking the AppleTV)
- Support for SATA disks of any size (mine have a 500GB)
- Build-in ftp server (Requires hacking the AppleTV)
- Build-in Samba server (Requires hacking the AppleTV)
- Support for mounting smb and nfs shares (requires hacking the AppleTV)
- Good support from vendor (actually fixes bugs and improves the product)
- Does not require iTunes
Cons
- User interface is very basic. Not ugly, just basic
- A bit more noisy (not fanless like the AppleTV)
- Playing music is not as sexy (again a very basic interface and does not support generating playlists)
- More expensive than the AppleTV. Without a disk the Tvix is roughly the same price as 160 GB AppleTV (In Denmark the cost of the AppleTV is somewhere around $600). And a 500GB disk adds another $100.
Which one is better? Unless you are a Apple f@nboi (which I am not) I say the technical features of the Tvix wins.