I would recommend using Journal Citation Reports (JCR). JCR will give you journal rankings, impact factors and citation data drawn from the most highly cited scholarly, peer reviewed journals. JCR includes journals from all areas of science, technology, and social sciences.
Choose "View a group of Journals" by subject category and on the next page select your subject from the drop down menu. Then under "View Journal Data" sort by "Impact Factor" or "Total Cites."