Standardized regression coefficients...different ways to do this, depending on what kind of variables you have (continuous, etc.). This simply involves z-transforming (mean=0, variance=1) each variable and then running the regression. All of your effects are then in standard deviation units. Each effect size (beta parameter) can then be compared to one another. A couple of Google results:

http://en.wikipedia.org/wiki/Standardized_coefficient

http://dss.princeton.edu/online_help...sion_intro.htm

Hope this gets you on the right track...