Check a domain name
Yet another one
InterNic Whois
Whois.net whois server
Check domain outside USA (at RIPE)
Networking tool
Check ip at ARIN server
a huge source of traceroute and more utils
Huge traceroute sites list
Monitorhost provide traceroute nslookup and more
RIPE net looking glass Allow you to do traceroute and AS as well
If you want to check a domain for its NS and errors this is the place
Domtools provide good domain check tool called dlint
Domain tools provide online tools
A good Util using Dig perform domain check
Another good tool
DNS Net Provide good explain on DNS and Bind
Subnet Mask util
Subnet mask and network calculator
RIPE provide subnet-mask table
Cisco Provide Subnet mask table as well
Test your Network for Smurf
test your network from the outside world
UnDotted IP to Regular IP converter
IP Address explain (good One)
Wireshark is a free Network Monitor
Wireless sniffer by UFASoft is also very good one
Old version of lot of well known softwares can be found here
Look for a non existed site ? try your luck here (with wayback machine internet arciver)