For anyone who does not know:  the von Neumann method involves counting results only half of the time ('HH', 'TT' are not counted).  So for every two coin tosses which are 'HT' or 'TH' you add 1 bit.  So 1 bit for every 4 coin tosses on average.

I have not tried it.  Sounds the most secure, but tiring too.