Other on demand scanners that could be recommended are hitman pro, and super antispyware, and emsisoft antimalware.
I recommend an additional scanner with MSE (Anvisoft Smart Defender, MBAM Pro, or Immunet.
I also recommend a firewall Comodo Firewall, ZoneAlarm Free Firewall, or Tinywall.
Windows Defender gets disabled by the MSE installer so it would not be in anti-spyware section.
Edit: Do you have any add-ons in Firefox? If you need any ideas you can check out my configuration: http://malwaretips.com/Thread-Malware-Maniac-Security-Configuration-Updated-June-2012