Surprisingly the best free one won't even stop everything. But the one in mind is now seeing emails about arriving in free email accounts namely Spyware Terminator found at http://www.spywareterminator.com/ that being the home page there.
The ST program has a mild firewall built into it making it better then many. Ad-Aware SE Personal and AVg 7.5 Grisoft's own free antivirus software work well together. Each one will find what the others miss.
