I've met Anderson Cooper and Samantha Brown.  Both were super kind and down to earth.  I met Martha Stewart at a book signing.  She was cranky, but had just signed hundreds of books, so I will give her the benefit of the doubt.  
Other celebs include:
Jeff Corwin
Jane Goodall
Tipper Gore
Julia Child
Bob Dole
A month ago, my husband and I saw Justice Sonia Sotomayor in the supermarket.  At first, he did not believe that it was her because she was dressed very casually and driving an economy car.  Then we heard her distinctive voice and watched as shoppers trailed her with their iPhone cameras.