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