All answers may be to some extent opinions, Forrest
A single firewall program, not two.
A single "resident" anti-virus program, not two.
As many anti-spyware programs as you like.
Provided that: auto-updating & "resident or real-time" protection features do not conflict.
In practical terms:
I use (considered anti-spyware)
- Lavasoft Ad-Aware Personal SE 1.05
- Spybot S&D 1.3
- Javacool's SpywareBlaster
- Webroot Spy Sweeper
- Microsoft Anti-spyware Beta 1
- Emisoft A-squared
- Pest Patrol
I update each "manually" and run each about once a week.
I use just Spybot's resident anti-spyware protection.
I'd consider mine just one opinion,
but I have run several other free ones that are uninstalled, too.