Incoming Exchange Filters

So with the plethora of new viruses being released almost daily I feel the need to try to step up my inbound security. Anyone know of a good inexpensive product that will filter out inbound (or outbound) messages? I want to be able to take the SARC alerts and create a new definition file to filter out the new viruses. It would be best if this product would also work with Exchange 2000 which we may or may not move to next year.