In this post you'll find some very interesting links about the nub-theory. Since many people ask for this from time to time, I'll ask Maureen or Redcin to pin this at the top.
http://images.google.com/imgres?imgurl=http://www.ultrasonografia.cl/us84/ARA1B&imgrefurl=http://www.ultrasonografia.cl/us84/ara.html&h=131&w=227&sz=15&hl=sl&start=72&um=1&tbnid=C6tusj_UY2Q4qM:&tbnh=62&tbnw=108&prev=/images%3Fq%3Dthe%2Bgenital%2Btubercle%2Bangle%26start%3D54%26ndsp%3D18%26svnum%3D10%26um%3D1%26hl%3Dsl%26sa%3DN
http://www.thefetus.net/page.php?id=1847
http://baby2see.com/gender/external_genitals.html
http://baby2see.com/gender/study_ultrasound.html
http://www.ingentaconnect.com/content/jws/uog/2006/00000027/00000006/art00005
http://www.blackwell-synergy.com/doi/abs/10.1046/j.1469-0705.1999.13050305.x
http://bjr.birjournals.org/cgi/content/full/76/907/448
http://www.ob-ultrasound.net/genderfaq.html