dsniff

allows to catch passwords traveling in clear text,

or just obfuscated !!!

supports more than 30 standardized / proprietary protocols:

FTP, Telnet, SMTP, HTTP, POP, poppass, NNTP, IMAP, SNMP, LDAP, Rlogin, RIP, OSPF, PPTP MS-CHAP, NFS, YP/NIS, SOCKS, X11, CVS, IRC, AIM, ICQ, Napster, PostgreSQL, Meeting Maker, Citrix ICA, Symantec pcAnywhere, NAI Sniffer, Microsoft SMB, Oracle SQL*Net, Sybase et Microsoft SQL.

strong items:

full TCP/IP reassembly,
support of asymmetrical routes,
auto-magic protocol detection,
storage in a Berkeley DB,
HTTP: QUERY_STRING and x-www-form-urlencoded parsing.