For antivirus? AVG has a free version (it tends to be kinda buried on their website). Clamwin had a pretty good reputation last I checked as well.

Other anti-malware options with free versions: Malware Bytes.

Note: Don't use more than one antivirus program simultaneously-- they can fight and screw things up. One antivirus program and one anti-malware program (Spybot or malware bytes) is good.