http://www.oneverify.com
is the newest on the market and seems to be the best since it's backed by
http://www.topbucks.com
and therefore the free option for 1 year (paid with $20) is accompanied by the 3 day trial subscription (and potential recurring - paid with 60%) to all straight or gay TB sites - that's a good incentive for surfers to stay, and for webmasters to earn for recurring.
Also,
http://www.cyberage.com
and
http://www.universalpass.com
are 2 good ones that I use.