I recently found this link while doing some very important online work (yeah right, I was looking for x-mas gifts). Anyways, this link is basically a .pdf of pocket reference guides on all your basic TCP/IP data broken down. I thought it was neat as I've used IDS's before and some of this info can help translate various packet data. So, check it out. I liked it. Tell me what you think of it.

http://www.sans.org/resources/tcpip.pdf
*note - I searched the forums and didn't see this link posted before, if it was, and I missed it then my apologies for being a dumbass