I recently replaced my hard drive and am looking for the best free anti-spyware /malware application to install. I already have an antivirus installed (Avast) so all I need is one for spyware/malware. I was using Spybot S&D before, but I've read that it isn't what it used to be, so I'm looking for something that is free, effective, and not a resource hog.

Your advice and suggestions are most welcome.