Neil deGrasse Tyson is the coolest astrophysicist around. Seriously, he makes the cosmos come alive and exciting. I first fell in love with the comos by reading Contact by Carl Sagan (a good read - I highly recommend it, it's even better than the movie!)
Also for those living in Philly, he will be speaking at the Free Library of Philadelphia on March 3rd @ 7:30pm for FREE. Come and learn about Pluto - The Rise and Fall of America's Favorite Planet (which apparently is no longer a planet).
Watch Neil on the Colbert Report discuss dark matter because Stephen doesn't see the color of matter.