Once upon a time (about 7 years ago) Beej's guides saved my life at work when trying to implement network stuff in C for a project at work I was in over my head on.
If there was more stuff like this in C-land I probably wouldn't have been clambering to get away from C and into more nurturing, sharing communities at the first opportunity.
Another relevant / extensive source is Unix Network Programming by W. Richard Stevens. Mostly relevant to Linux / Unix systems, but still worth a read.
Edit:
Matter of fact he lists it as the first reference under "More References"
If there was more stuff like this in C-land I probably wouldn't have been clambering to get away from C and into more nurturing, sharing communities at the first opportunity.
Really cool to see he's keeping it up to date.