Does anyone know of a software implementation of RAID 10 that will work on a Windows Server 2008? Specifically I'd like to use it on a virtual instance running on Amazon's EC2, connected to EBS disks.
Windows software RAID doesn't support RAID-10. I've never heard of third-party drivers for Windows software RAID and, frankly, I think I'd be afraid of them if they did exist. (They'd have to be debugged and battle-tested before I'd even think of using them...)
There is no reason to create a RAID-10 configuration in the AWS environment. AWS is already providing disk redundancy in the EBS layer.
It can be worth creating a RAID-0 configuration. EBS is notoriously slow and striping your drive across multiple EBS volumes can significantly boost performance.