Hi Summer, don't know if you noticed it or not in my immediate family tree, but my daddy's sister married my mother's brother (say that too fast and you think you are losing it). I find it interesting that someone said in the comments that the double first cousins are closer than siblings. I am an only child, so have always felt like my double first cousins were my older "brothers", :).
There is another instance in my family where my grandfather Towns' sister, married my grandmother Towns' half-brother.
I believe there are other instances, I just haven't made a note of all of them yet.