As every second Tuesday of the month, Microsoft has already published the September security bulletins.
Below you can see the description of the 4 bulletins rated as critical, as well as the links:
More info: Microsoft Security Bulletin MS08-054
More info: Microsoft Security Bulletin MS08-052
More info: Microsoft Security Bulletin MS08-053
More Info: Microsoft Security Bulletin MS08-055
We recommend you to update your system as soon as possible.