|A Black Hole|
Black Holes are massive objects occupying a tiny volume in space. When a super-massive star (many times larger than the Sun) stops sustaining enough nuclear fusion at its core to support its size, its mass may collapse into itself and form a Black Hole, sucking in everything around it. Our Milky Way galaxy spirals around a super-massive Black Hole at its center.
Since nothing can escape from the incredible gravitational pull of a Black Hole (even light itself), scientists can only speculate on what would happen to a person falling into a Black Hole. However, it does seem evident that the crushing gravity would not be kind to your body. Soon after passing the Event Horizon, the point of no return, your body's atomic structure would be ripped apart. The parts of your body closer to the singularity experience a stronger gravitational pull than the parts of your body further away from the singularity. This "tidal gravity" creates a differential gravitational pull on your body that literally stretches you out as you fall in. Alas, the rack of space-time is unforgiving to even the most pliant mind, and ultimately it's impossible to keep yourself together.
Interestingly, getting sucked into a Black Hole doesn't necessarily mean all trace of you is permanently erased. Physicist Stephen Hawking recently theorized that Black Holes emit minute amounts of radiation energy, like quantum information signatures of the stuff pulled in. So-called "Hawking Radiation" retains the information characteristics of the stuff that the Black Hole gobbled up; if a carbon atom gets sucked into the Black Hole, eventually the energy equivalent of a carbon atom will spew back out as Hawking Radiation. The information of the universe is conserved. So, at least in quantum theory, you could be reconstituted bit-by-bit if an outside observer were able to interpret Hawking Radiation and piece you together.
Cosmologist Ted Bunn's Black Hole FAQ (Frequently Asked Questions) offers many expanded answers: http://cosmology.berkeley.edu/Education/BHfaq.html