This popular and well-engineered suite by Dug Song includes many tools: dsniff, filesnarf, mailsnarf, msgsnarf, urlsnarf, and webspy passively monitor a network for interesting data (passwords, e-mail, files, etc.); arpspoof, dnsspoof, and macof facilitate the interception of network traffic normally unavailable to an attacker (e.g, due to layer-2 switching); and sshmitm and webmitm implement active monkey-in-the-middle attacks against redirected ssh and https sessions by exploiting weak bindings in ad-hoc PKI. A separately maintained partial Windows port is available here. The suite suffers from the lack of any updates in the last decade, but it is still a great toolset for handling your password sniffing needs.