You can use any backup software that has a client piece that is installed inside of the VM. That will back up all of the VM data.
If you also want the VM config then you will need to use something Hyper-V aware that runs from the parent partition. You can use Windows backup or System Center Data Protection Manager, or a number of third-party backup tools.
If your servers are running Hyper-V 2008 R2 and are in a cluster using Cluster Shared Volumes then it becomes much more complicated. System Center Data Protection Manager 2010 will correctly handle this (currently in beta), but in the meantime it's going to be ugly. There may be third-party backup tools that support backups of VMs on CSVs, but I don't know of any offhand. I have also heard that it is possible to make backups of VMs on CSVs IF the backup runs from the host that owns the CSV. I haven't tried it though, and since that can change across reboots it becomes a cumbersome mess to try to write some scripts that do this well.
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CompTIA A+, Network+, Server+, Security+
MCTS:Windows 7
MCTS:Hyper-V
MCTS:System Center Virtual Machine Manager
MCTS:Windows Server 2008 R2, Server Virtualization
MCSE:Security 2003
MCITP:Server Administrator
MCITP:Enterprise Administrator
Certified Quest vWorkspace Administrator