Enumeration
> ike-scan ( http://www.nta-monitor.com/ike-scan/ )
> ike-probe ( http://www.ernw.de/download/ikeprobe.zip )

Brute-Force
> ike-crack ( http://ikecrack.sourceforge.net/ )

Reference Material
> PSK cracking paper ( http://www.ernw.de/download/pskattack.pdf )
> SecurityFocus Infocus ( http://www.securityfocus.com/infocus/1821 )
> Scanning a VPN Implementation ( http://www.radarhack.com/dir/papers/Scanning_ike_with_ikescan.pdf )