Good question and something to look at when interviewing for residency positions. The short answer is use the case volume as a gauge to assess programs on paper, but talk to the residents when interviewing and get a sense of their "actual" experience.
Long answer: Recently the ACGME increased the volume to 750 required cases to graduate, up from 500. Then it is broken down into various sections: Vascular, Endocrine, Peds, Non-op and Operative trauma, Laparoscopic (basic and complex), etc. When I interviewed 4 years ago the range was 700-1400+. Most fell between 950-1100. These numbers are on listed on the programs websites. If not, they usually give them to you at the interview. However, remember these were graduating numbers pre-80 hour work week, which will cause an adjustment. When I made my match list, I put 1000+ (average chief resident) as my cut-off.
Another factor to consider is type of cases. If you know what you want to do then choose accordingly. i.e. Cardiothoracic look at the experience. If you want to do trauma...pick a level I regional center and don't go to a community based level II or lower trauma center.
One final thought, take the reported case loads with a grain of salt. Residents log cases differently, and may be a institution phenomenon. A few examples are: logging a case if they scrub, others log if they dictate the case, and some log if they do more than 50% of the case. Also, large university programs with fellows on every service means the chiefs may be acting more like first assistants than junior surgeons. When on an interview, ask the residents..."When you do this (insert type of case), how much do you do and how much does the attending do?
