ISI's Journal Citation Reports and Washington & Lee's Law Journals: Submissions and Ranking can show you the most frequently cited and highest impact journals in law, criminology and penology.
Sources for finding citation counts and subsequent cited papers
Google Scholar Metrics
"Google Scholar Metrics enable authors to gauge the visibility and influence of recent articles in scholarly publications. Scholar Metrics summarize recent citations to many publications, to help authors as they consider where to publish their new research.
To get started, browse the top 100 publications in several languages, ordered by their five-year h-index and h-median metrics. To see which articles in a publication were cited the most and who cited them, click on its h-index number to view the articles as well as the citations underlying the metrics.
To browse publications in a broad area of research, select one of the areas in the left column. For example: SOCIAL SCIENCE.
To explore specific research areas, select one of the broad areas like SOCIAL SCIENCE, click on the "Subcategories" link and then select one of the options. For example, "Top publications - Criminology, Criminal Law & Policing" ...