In my Critical Reading and Writing class we read Gorgias' Encomium of Helen. It's only like four pages long and definitely one of my favorites.
Here's a link if you'd like to read it: http://www.phil.vt.edu/mgifford/phil2115/Helen.htm
Here's a link if you'd like to read it: http://www.phil.vt.edu/mgifford/phil2115/Helen.htm