The oldest fraternity at Washington and Lee is Phi Kappa Psi. It's Virginia Beta (I think) and I believe is their second overall chapter, founded 1856 (I think). I'm sure Russ will correct me if I'm wrong.
I'm pretty sure the next fraternity was KA Order, which was founded here during the Lee Presidency (1865-1870).
The oldest three sororities on my campus were all colonized in the same year, 1989. They are Kappa Kappa Gamma, Kappa Alpha Theta, and Chi Omega.