I've had great experience with Google Scholar Alerts. To use them, go to scholar.google.com and search for any term. In the results page, you will see a link to
Create Email Alert. Click on that and create the alert to send you notifications.
One very good use of this is to follow specific papers. For example, I have a star paper of mine that I'm currently extending and I like to keep track of who is citing this paper. So, I search for the paper on scholar. In the results page (just under the result for the paper I'm concerned with), there's a link
Cited by 'n'. Click on that and you get results for only those papers that cite this article. Now, create an alert on this page. This way, whenever someone refers to this paper (and Google finds out about it), you get an email. Do this for all the important literature in your field and Alerts will make sure you are kept abreast of your field.
Never miss out on an important finding!