Practical Packet Analysis, 2nd Edition

The second edition of Chris Sanders' Practical Packet Analysis is about twice as large as the first edition and twice as useful.

I learned Wireshark in the traditional manner: got annoyed with tcpdump, installed Wireshark, and started poking menus and buttons until I got a result. Chapters 1-5 of PPA takes you through the important menus and buttons. There's not much you can do to make descriptions of software options interesting, but Sanders demonstrates real-world uses as he goes along...