Looking for a good coprate antivirus / antimalware solution.

I just started for a company that is quickly.  They have around 100-200 windows computers (XP and Windows 7) and Windows Servers, but they are spred out over 11 diffrent locations.  They have been buying Norton AV oem with all the new computers, but they are running out at diffrent times and most of the time I don't know about it.  I need a solution that is scalible and easy to manage (I am the only IT guy).  It would be nice if it was easy enough for me to send out a email and have the end users install it and just contact me if they have a issue.  Any ideas would be apreshated.  Thanks in advance.