Fourthed; again, use almost every day. Conman and powerman are great.
Conman: Serial consoles, IMPI serial consoles, write your own wrapper if one doesn't exist.
Powerman: Can control just about everything out there. Again, write your own if it doesn't exist. Can even "manage" power on a VM host. You might have to write your own wrapper though (basically a remote shell that runs virsh commands). I know we have a script here, but I don't think I'm allowed to put it in public. It uses rsh to connect to the VM host (KVM) and then runs virsh domstate for power status, and virsh start/virsh destroy for on and off.