These are the professional organizations most used and recognized by PC(USA) collegiate ministers:

Presbyterian Organizations
PACHEM (of course) - The organization for all those engaged in PCUSA collegiate ministries.
PCCA - The Presbyterian College Chaplains Association. For those serving as higher education chaplains, either as Presbyterians, or as the chaplain at a Presbyterian church-related college.
Ascent Network - An informal affiliation of primarily congregation based, evangellical,campus ministers. Usually have an annual conference at one of the member churches in the spring.

Ecumenical Organizations
NCMA - The National Campus Ministry Association. Ecumenical organization, primarily of campus ministers. They have an annual conference in the summer, useful for any campus minister, and a web site with resources for dues paying members.

InterFaith Organizations
NACUC - The National Association of College and University Chaplains. Includes Jewish and Muslim chaplains. Annual conference in February.
ACURA -  The Association for College and University Religious Affairs. Composed of chaplains, deans of religious life, directors of religious affairs, and religious life administrators. Meets annually in October at one of the member institutions.