AdAge.com - News, features, and entry-level (as well as experienced) positions. Neat site.
Adweek - Most of the classifieds are for experienced professionals, but the news section is a MUST for anyone looking to break into the field.
Creative Jobs Central - It costs to join, but it has job postings in everything from acting to sports... might be worth it!
J-Jobs - Berkeley Grad School of Journalism job and internship board.
Journal of Young Investigators - JYI's mission is to improve undergraduate science training by providing innovative, high-quality educational experiences in science writing, publication and the peer-review process.
Public Relations Society of America - the world’s largest and foremost organization of public relations professionals. PRSA provides professional development, sets standards of excellence and upholds principles of ethics for its members and, more broadly, the multi-billion dollar global public relations profession.
Society for Technical Communications - Members of this organization include technical writers, editors, graphic designers, multimedia artists, Web and Intranet page information designers, translators and others.