This tool provides a demonstration of the HTTPS stripping attacks that I presented at Black Hat DC 2009. It will transparently hijack HTTP traffic on a network, watch for HTTPS links and redirects, then map those links into either look-alike HTTP links or homograph-similar HTTPS links. It also supports modes for supplying a favicon which looks like a lock icon, selective logging, and session denial. For more information on the attack, see the video from the presentation below.
To get this running:

Flip your machine into forwarding mode.
Setup iptables to redirect HTTP traffic to sslstrip.
Run sslstrip.
Run arpspoof to convince a network they should send their traffic to you.
That should do it.

How does this work?

First, arpspoof convinces a host that our MAC address is the router's MAC address, and the target begins to send us all its network traffic. The kernel forwards everything along except for traffic destined to port 80, which it redirects to $listenPort (10000, for example).

At this point, sslstrip receives the traffic and does its magic.

Changes in 0.2 (02/25/09)

Fixed the listen port command-line option to actually work.
Changes in 0.1 (02/21/09)
Initial stripped-down public release.

http://www.thoughtcrime.org/software/sslstrip/
http://securitytube.net/SSLstrip-Tutorial-video.aspx