Some tools you may (will) want to add to your collection

Router Commander
http://www.majorgeeks.com/files/details/router_commander.html

Setup a Static IP Address
http://portforward.com/help/setup_static_ip_address.htm
Open Port Check
http://portforward.com/help/portcheck.htm
Try the Port Forwarding utility (not free)
http://portforward.com/store/PFCSetup.exe

Open Visual Traceroute (Windows/Linux/Mac)
http://sourceforge.net/projects/openvisualtrace/ 
vTrace
http://vtrace.pl
3d Traceroute
http://www.d3tr.de.nyud.net
GeoData IP (Opera plugin)
http://code.highspec.ru/gd4ip_about.htm
WIP Geo-tools for Firefox
https://www.wipmania.com/plugins/

IPv6 Readiness Test
http://www.thinkbroadband.com/ipv6/test-ipv6.html
IPv6 Speed Test
www.ipv6-speedtest.net

DNS Benchmark
www.grc.com/dns/benchmark.htm

Windows own network info does not give you much feedback, so..
LanLights (up to XP)
www.paulmather.net
tbbMeter (very useful for mobile and limited accounts)
www.thinkbroadband.com/tbbmeter.html
AddGadgets Network Meter (Vista and up)
http://addgadgets.com/network_meter/

Tweakers
SpeedGuide.net
Analyse: www.speedguide.net/analyzer.php
Optimise: www.speedguide.net/downloads.php
www.speedguide.net/articles/windows-7-vista-2008-tweaks-2574

Cablenut
www.cablenut.com
www.j79zlr.com/cablenutXP2k.php

BT Network Optimiser (basic)
http://support.zen.co.uk/kb/Knowledgebase/Broadband-MTU-Tools

SpeedNeed (v.basic. updated for Win7)
http://sourceforge.net/projects/speedneed/

Test your tweaks
http://www.dslreports.com/tweaks

Tools collections
www.all-nettools.com/toolbox/
http://mabsoft.com/nettools.htm
http://thedatalist.com/pages/Web_Trace_Tools.htm

Internet Router traffic
www.internetpulse.net
www.dslreports.com/routerwatch
http://internettrafficreport.com
www.akamai.com/html/technology/dataviz1.html