Effective? Yes Freeware? No.
You should have one AV and (optionally) one anti-spyware with real-time protection.
You can have several anti-spyware scanners, e.g., Spybot Search & Destroy, Ad-Aware free, Avg Anti-Spyware free, a-squared free.
If you want real-time anti-spyware protection, the free options are Windows Defender (poor detection) or Spyware Terminator.
The paid options (better detection rates) are Spysweeper, SpywareDoctor or CounterSpy.