tracetcp

Winpcap: Windows Packet Capture library. This is required by tracetcp in order to function.
tcptraceroute: A traceroute program that uses TCP packets for Linux/Unix written by Michael C. Toren. This program (and the fact I couldn't find a Windows equivalent) was the inspiration for tracetcp.
Ethereal: A fantastic network protocol analyzer, that has saved my bacon numerous times. Anyone writing or supporting networked software should use this program.
Winsock FAQ: Very useful programmers information about Winsock programming.
Microsoft's Raw TCP/IP sockets Documention: Microsoft's rather short documentation about Raw sockets under Windows (not especially useful any more....).
IANA's list of port numbers: A handy list of the Well Known and Registered port numbers.