http://www.messagelabs.com/resources/mlireports

http://www.securityfocus.com/

http://www.symantec.com/norton/security_response/threatexplorer/index.jsp

https://www-secure.symantec.com/connect/symantec-blogs/security-response/all/all/all/all/en

This is what i use personally.

Even this will be handy

http://www.threatexpert.com/

http://www.securitynewsportal.com/

http://www.microsoft.com/security/

http://technet.microsoft.com/en-us/security/default.aspx

Hi Sheri

There is also another easier way to get the latest security information and new through the SEPM console.

Login to the Symantec Endpoint Protection Manager console

On the Home page, under the Security response section, there are a few links that you can click on like

Security alerts
Latest threats
Security Focus

These should give you ample information about latest security and management news.

Hope this is helpful

Thanks :-) 

Also, try to get on mailing lists from your software vendors that will tell you about security notifications such as Microsoft (http://technet.microsoft.com/en-us/security/dd252948.aspx)

This way you're always aware of new threats that are out and can take more immediate actions to patch up your systems.