Don't bother with any of the bloated (and expensive) all-in-one security suites, just get a freeware firewall like Jetico or Ashampoo and a freeware AV like Avast or Antivir (for optimal performance don't allow realtime scanning, just manually scan downloads).
Use Opera or Firefox and some kind of adblock mod and there is a very good good chance you will remain free of spyware. Memory resident spyware scanners are notorious resource hogs, so I'd steer clear. Again, manually scan occassionally if it makes you feel better.
Registry cleaners are pretty much worthless. At most you are going to strip out maybe 30kb of "junk" and there is a real risk of causing damage. Is it worth it?
So called memory optimisers are a waste of space too. All they do is ship stuff out to the swapfile. Avoid.
For the record I use Ashampoo firewall, NOD32 (manual scans only), Opera, Winpatrol (checks for items adding themselves to startup) and Perfectdisk (IMO the best defragmenter). I've never had a virus or malware outbreak in 8 years of computing.