I've been using a BMX layback seatpost. The setback would be pretty extreme for most people but works well for me.

Here is one similar to the one that I took with me.
http://cgi.ebay.com/VINTAGE-BMX-1980...item45f0ea19ca

Here is another similar to what I have on my current mountain bike.
http://cgi.ebay.com/NEW-generic-chro...item4a9ec183b8