One of my simplest blog posts has also been one of my more popular posts. It visually demonstrated the difference between the number of states that allow gay and lesbian couples to marry vs. the number of states that allow first cousins to marry. Since then, there has been one notable update (New York State now allows gay and lesbian couples to legally marry.
Check out this updated map directly below (click on the picture and you'll get a better view):
Not only does it demonstrate the the vast number of states that allow first cousins to legally marry as opposed to the number of states that allow gay couples to marry, but it also shows the minimum age requirement for the different states. For example, the good people of Alabama are protected from the horror of homo-fidelity, but you can still marry your 14-year-old first cousin (as long as s/he is a member of the opposite sex).
Just something to think about next time someone around you starts spouting off about marriage equality for gays and lesbians and the slippery slope.