[ajross]

Stevens's Unix Network Programming is the classic. Any edition will do -- quite frankly the first is clearest. He gets coverage-happy (STREAMS, seriously?) in the 2nd and the 3rd (completed by another author after Stevens's death) is just plain too big.

[void-star]

No, really. Whatever else you refer to, make sure you include Stevens' UNP. (edit: agree also, 1st edition is the best by far)