Black holes and neutron stars won the poll by a hair. So here is my small info dump on them. Most of these concepts are taken from what learned in my textbooks, lectures, and classroom discussions. I am by no means an expert on the subject, I don't go pushing around equations and numbers about them, but I am probably more familiar with some of the subject matter then most. That said, I will try to avoid the math, and just provide some interesting information about these cosmic oddities. I also provide link to wikipedia in some places, because generally it's the easiest thing to link for information on this stuff.
Also, a new poll should be up, so those who wanted dark matter, you get to try again. Same with anyone else interested in the other areas. I replaced Black Holes/Neutron Stars with...