The Washington Monthly has a ranking of universities which puts an emphasis on such factors as “social mobility.” The top schools in its ranking are UC-San Diego, UC-Berkeley, and UCLA in that order. Perhaps more interesting than the rankings is that you can look at such factors as the percent of students receiving Pell grants.
For details, go to http://www.washingtonmonthly.com/college_guide/rankings_2010/national_university_rank.php