National Vulnerability Database (NVD) - United States government's National Vulnerability Database provides additional meta-data (CPE, CVSS scoring) of the standard CVE List along with a fine-grained search engine.
US-CERT Vulnerability Notes Database - Summaries, technical details, remediation information, and lists of vendors affected by software vulnerabilities, aggregated by the United States Computer Emergency Response Team (US-CERT).
Vulnerability Lab - Open forum for security advisories organized by category of exploit target.
Vulners - Security database of software vulnerabilities.
Vulmon - Vulnerability search engine with vulnerability intelligence features that conducts full text searches in its database.
Zero Day Initiative - Bug bounty program with publicly accessible archive of published security advisories, operated by TippingPoint.