Internet Tools All-In-One Site

[Yo Mama]

http://www.phaster.com/find_info_net_traffic.shtml

Not your usual DNS site -- this one is a haxor site, but the tools are useful for trying to track down IP address information and other things that may need attention while researching a CT.

includes the following (and many other services):

Domain Lookup
Email Dossier
Finger
IP Location
IP Targeting
MAC Addresses
NMap
NSLookup
Ping
Port Number
Reverse DNS
Trace Route
Traffic Rank
Uptime
Whois

Internet Storm Center status chart access (for tracking crackers around the world)

And much, much more!

Extremely comprehensive and useful.