Network Admin Tools:
* Packet Analyzer - Wireshark
* Graphical Ping Tool
* Port Scanner
* MAC Scan
* Netflow Listener
* SNMP Scanner
* WMI Scanner
* Switch port mapper
* TFTP Server
* WhoIS Lookup
* Traceroute

To DOWNLOAD all the above tools, click here.

AntiVirus, Firewall and AntiSpyware:
Norton
McAfee
AVG
PCtools
Comodo
Zone Alarm
Sygate
Panda
Avast
KasperSky
LavaSoft
Windows Defender