HTTP Strict Transport Security (HSTS) will soon be finalized and available in an IETF standard. The request for comment (RFC) is at version 11 and the IESG has put out a last call for comments.
HSTS is a security policy mechanism where a Web server tells a supporting browser that it can only connect to it over secure connections (i.e., SSL). HSTS allows website operators to force secure connections with users that are using an HSTS-supporting browser. Supporting browsers include: Google Chrome 4+, Firefox 4+ and Opera 12.
I have spoken about HSTS before in a previous blog post and will update again once it has been finalized.
Updated October 3, 2012: Jeff Hodges announced that HSTS has been approved by IESG as a proposed standard RFC.
Updated November 21, 2012: HSTS has been published as RFC 6797.