Journal TOCS(or, Table Of ContentS) is a great way to keep up to date with your favorite research journals.  This service allows you to search out over 14,000 journals using keywords in your subject area, as well as finding journal articles.  You can also pick out the journals you want to keep close track of and have the updated table of contents list of those journals emailed right to you.  Journal TOCS includes widely regarded periodicals such as Nature, Science and JAMA.