I am a member of Phi Sigma Sigma (Spring 00) a social org, also a member of Tau Beta Sigma (Fall 00) honorary sorority for college band members and Beta Sigma Phi - a womens organization for women 18 and up, not affliated with a school. BSP chapters CAN be on a campus though (check it out, always an option and really easy to start a chapter!)
My Phi Sig two little is in like 20million orgs and I told her Im buying her a shirt with the greek alphabet on it so she can wear all her orgs.
You can be in ONE social org, and ONE honorary PER DEPARTMENT (I could not rush Kappa Kappa Psi, but I COULD be made honorary) - then you can also go on to things such as professional orgs, special interest orgs, service org.
So at MY school one could say be a Zeta (social), in TBS (honorary-Band), SAI (special interest on our campus), Alpha Phi Omega (service), a language honorary, KDPi (ed honorary), Order of Omega etc... really you can be super greek, but also SUPER poor and busy!!