Worldwatch (which has an excellent population portal) is putting out a whole issue of its magazine on the topic Population and its Discontents. The articles (only a few of which are free to view, unfortunately -- what's up with that, Worldwatchers?) cover a lot of provocative ground: the challenges created by the confluence of swelling populations and unsustainable forms of affluence; an overview of population trends to date; the emergence of the "youth bulge" in developing nations; why aging populations and declining fertility rates in the developed world are not a problem; and speculations on the possibility of extremely large mass-migrations in coming decades. Might be interesting. Might also be better to just check out the resources Alan recommends in Indicators are Reality, which at least are free.