Vista Ultimate - $399USD ($259 Upgrade)
The only version larger than Ultimate is Enterprise, which is like the Business edition on crack. It includes various hardware based security measures to assure for good uptime. Ultimate is the version you will want to consider should you think $400 is not a lot of cash to hand over for a new OS. Below, you can see the list of what Ultimate -does- include, which Home Premium, the next competitor, does not.
* Ultimate's Advantages Ultimate "extras", which could include games and special utilities
* BitLocker hard drive encryption software
* Advanced complete system backup tool
* Windows Media Center with Xbox 360 capabilities
* Same business apps as included in the Business edition
* Automatic "Shadow" copies of your documents
* Remote Desktop
* Advanced group policy editor
* Ability to run UNIX-based applications (through SUA)
* Support for dual CPU's or 128GB of memory
* Encrypting File System (EFS) support
* Support for resyncing files for getting work done while offline