For the areas they cover, being a member of the relevant IEEE group can be useful (I guess ACM probably does something similar but I'm not a member). For one of the groups I'm in, I receive a pamphlet every few months that summarizes a ton of papers in the field and a CD with the full content on. (It's all online as well, but I know I'd never remember to actively check there.)

You may also find the relevant section of http://arxiv.org/ useful as well. For example, http://arxiv.org/list/cs.SE/recent

Once you have identified the most significant individuals on a field, you can use google scholar alerts to get notified when they publish something new. (http://scholar.google.com/scholar_alerts?view_op=list_alerts). In the case of machine learning that would be Geoffrey Hinton, Yann LeCun, Yoshua Bengio, Andrew Ng (this list is not exhaustive of course).

In other sciences, you'd follow some leading journals. In computer science, you follow some of the leading conferences (and hope that the conference publishes the proceedings in some place that your university has access).

get suggestions from more informed people (e.g reading groups, professors, news aggregators :p ).

work smart, not hard.