'For The Women' is the only decent 4women paysite i can think of at the moment:
http://www.purpledollars.com/
The other 4women sites that i've looked at usually look like the usual cookie cutter paysites. Most likely created by a geeky designer dude who has no idea how the female brain works.
Some women fantasize about having a 3-some with 2 other guys.. [A few of the more open ladies that I know have admitted this to me.] Therefore, I predict bisexual sites could work as well.
The paysite 'Three Pillows', i've heard, is a good bi site:
http://www.bibucks.com/ I think It seems reasonable enough to assume that some ladies may dig it.
I hope that this gives you somewhere to begin,
Josh