Several sites provide CVSS scores for security vulnerabilities, or provide calculators for generating CVSS scores, some of which are listed below.
NIST's NVD site provides a comprehensive and searchable list of security vulnerabilities, with CVSS scores
Information is also provided via data feeds
IBM X-Force CVSS score all of their alerts
FIRST CVSS calculator
Available in the sub-menu on the left.
Information-Technology Promotion Agency, Japan