.mdf and .ldf

Those are sql extensions 

Jeremy is Correct

Great, thanks guys.  Is there any centralized resource for recommendations for extensions.  Obviously all environments are different but it is worth the ask.

 You can refer following docs for recommended exclusions.
About the automatic exclusion of files and folders for Microsoft Exchange server and Symantec products
http://service1.symantec.com/support/ent-security....
How to Verify if an Endpoint Client has Automatically Excluded an Application or Directory
http://service1.symantec.com/support/ent-security....
Antivirus exclusions that should be set on a Microsoft 2000 or 2003 domain controller
http://service1.symantec.com/SUPPORT/ent-security....
How to Verify if an Endpoint Client has Automatically Excluded an Application or Directory
http://service1.symantec.com/SUPPORT/ent-security....
How to exclude SQL files and folders using Centralized Exceptions
http://service1.symantec.com/SUPPORT/ent-security....
Exclusions required to run Symantec Endpoint Protection with Windows SharePoint Services 3.0 or SharePoint Server 3.0
http://service1.symantec.com/SUPPORT/ent-security....
Configuring Symantec Endpoint Protection exclusions for Microsoft Forefront
http://service1.symantec.com/SUPPORT/ent-security....

You can refer following docs also
Guidelines for choosing antivirus software to run on the computers that are running SQL Server
http://support.microsoft.com/kb/309422
Client computers are unable to receive addresses through DHCP after installing Symantec Endpoint Protection
http://service1.symantec.com/SUPPORT/ent-security....
Preventing Symantec Endpoint Protection 11.0 from scanning the Microsoft Exchange 2007 directory structure
http://service1.symantec.com/SUPPORT/ent-security....

I recommend this list:

pagefile.sys

Oracle: .dbf
MSSQL: .ldf, .mdf and .ndf
Lotus Notes: .ntf and .nsf

For Hyper-V, refer here: http://blogs.msdn.com/virtual_pc_guy/archive/2009/...