What's a good packet sniffer for OS X?

Here are some that I really like:

Eavesdrop: http://www.baurhome.net/software/eavesdrop/
Ettercap: http://ettercap.sourceforge.net/
KisMAC: http://kismac.macpirate.ch/about.php

I still have yet to find a remarkably fast packet sniffer, but these are certainly satisfactory.

eavesdrop works pretty nice, i must say that the prementioned Cocoapacketanalyzer is now working decent, i’ll just test it some more, thanks anyway :)

What’s a packet sniffer?

a packet sniffer basically inspects every “packet” of data that comes through on the network and “sniffs” it, so it doesn’t use it, but just saves a copy of it, you can find out a lot of usefull information, and also for some, “evil” purposes

If you have Leopard, you already have tcpdump available in Terminal. Wireshark is another option, although I believe it requires an Intel Mac. If you know a bit about a byte, you can compile Snort.