There are several freely available sources that attempt to asses the scholarly impact of individual journals. The value of these metrics can be controversial, so be sure that your evaluating committee considers a measure valid before using it.
Google Scholar Metrics
Evaluates journals based on analysis of the last five years of articles. Excludes journals with less than 100 articles during the five-year period, as well as journals with no citations.
An attempt at a more sophisticated measure of journal impact than a simple ranking metric. Explores two new measures called Source Normalized Impact per Paper (SNIP) and SCImago Journal Rank (SJR).
A journal ranking service covering the natural and social sciences.