Apologies if this has been done ad nauseum.
After some experimenting, I have, for the nonce, settled on this lot:
Comodo firewall
Avast AV
Spyware Terminator active anti-spyware
Adaware spyware scanner
They seem to work OK together. How much of a drag they put on system speed I can't really say due to the variable speed of my internet connection.
Supplemented by at least a once-a-week scan at Trend Micro Housecall.