iNFOSYSSEC hosts the most complete collection of web-based network information tools I've seen in one place. It's free, and indespensible to any technophile needing to do some network diagnostics, or anyone wanting to quickly research domain names.

  • Smart Whois
  • NSLookup and Reverse Lookup
  • Anti-Spam Multi-tool
  • Server Response Time
  • HTTP Headers
  • Company Factsheet
  • NetCraft Domain Reporter
  • Network-Tools.com "multi-tool"
  • Name Server Lookup
  • Usenet News Author Profile
  • AnalogX DNSDig
  • Dig It! (was: Multi DNS Tool)
  • SMTP Relay Check
  • Realtime Blocking List Check
  • ARIN Whois
  • (IP Registry)
  • IP-Range DNS Query
  • Demon.Net Tool Array
  • RWhois Query
  • MX Lookup
  • Ping
  • IP Lookup
  • Test Email
  • Tracemap and Visual Trace Route
  • Bandwidth Test

Check it out at  http://www.infosyssec.com/infosyssec/ipsectools.htm