The website of this NGO contains numerous databases and publications and statistical series on foreign and international labor issues.
The NBER is a "private, nonprofit, nonpartisan research organization... committed to undertaking and disseminating unbiased economic research among public policymakers, business professionals, and the academic community." The web site makes available working papers, data sets, and online versions of selected older books.
Overall, lots of European data- HR and otherwise. Great section where you can look at OECD documents by country or by subject. Subjects include: best practices, case studies, manuals, scores and methods, and other valuable information.
SHRM is the primary professional organization for HRM practitioners. Its web site provides information on every aspect of HR, including OSHA, the implications of mergers and acquisitions, research articles, job postings, and more. Some content is free; access to the whole site is one of the benefits of student membership.