CCleaner is good for clearing the crap (thus the name) from your system, but does no real-time protection. I recommend it for light system housekeeping - but that is it.
Avast! is really heavy like AVG and is a menace on resources - especially on RAM. I would go for the lightest AV you can get - depending on your surfing habits. If you download a lot of stuff, you need something robust. I would visit TrendMicro and see what they have. SpyBot is one of the best free adware you can get - but Ad-Aware is usually sufficient and would be my only preference.
I am a stickler for resource conservation, so I go as light as I can go and avoid pirate software, cracks and so forth.
This is a good rule for anyone to follow: If you ever get a scareware message box saying 'your computer is infected, etc.' Calmly close the browser using TASK MANAGER. Click on nothing. Behave as though your browser just crashed. You can save a lot of trouble from java trojans that try to get in that way. They call it scareware for a reason.