See how one answer just brings up another question? :D
Actually, a black hole is more like a trash compactor - INDUSTRIAL GRADE!
Everything gets really compressed, so that there are no spaces between atomic particles.
The most dense object other than a Black Hole is a neutron star.
“A typical neutron star - if there is a typical one - has the density of about 3.7×1017 to 5.9×1017 kg/m3. The Earth for comparison has a density of 5.515 g/cm3
To put that into perspective, a neutron star has the mass of the entire human population, squashed down to the size of a sugar cube, or one teaspoon (5 milliliters) of neutron star would have 900 times the mass of the Great Pyramid of Giza.
Or imagine squeezing 50 million elephants into a thimble. That is the density of a neutron star.”
http://wiki.answers.com/Q/What_is_the_density_of_a_neutron_star
http://www.astro.umd.edu/~miller/poster1.html
http://www.physicsforums.com/showthread.php?t=425095
More info about black hole that you may want to know.
:-)
http://www.youtube.com/watch?v=0hyHtBtRXzo
(turn your speakers DOWN!)
Black Hole Neutron Star Collisons; Density Field