How to reset OS X 10.8 to boot? I ran the dd command on /dev/rdisk1 and now OS X is not starting.

Is it possible to recover the OS? I have access to recovery mode, but Disk Utility says that the disk is fine.
You can Erase the disk using Disk Utility (open Disk Utility, select the disk, then the Erase tab, and click Erase), then use the Reinstall OS X option in the Recovery HD utilities list, following the instructions as a normal OS X install.

Alternatively, use Internet Recovery by booting with ⌘⌥R.