I'm going around to many sites where I trust the information, particularly when it comes to protecting my computer, and asking for a list of recommended protection programs. This includes registry cleaners, cache cleaners, anti-maleware, anti-spyware, defraggers, anti-virus, firewalls, and various scanners and other optimization programs. Normally I would simply go to one specific site I've used before to save my computer from the brink of death, but since this time I'm doing this to help protect someone else's computer, I'm asking everyone and will weigh the answers I get against each-other.

For the record, the programs I've been recommended before are listed below, most of which (unless noted) I use right now either constantly or regularly depending on if they're on-demand protection or not. I will also list the current programs the other person uses after my personal list. All programs are completely free or at least the free version, and please keep in mind neither I nor the other person I'm helping can afford to purchase protection programs. Also, the other person wishes to clean and protect several computers in their household, varying from XP to Vista. I personally run XP.

Recommended to me from various sources

Currently on my computer
avast! Antivirus
Malewaerbytes' Anti-Maleware
SpywareBlaster
CCleaner
Puran Defrag
Housecall
HiJackThis!
Windows Firewall
Gamebooster

Not on my computer, but used in the past or recommended
Webroot Desktop Firewall
Outpost Free
SUPERAntiSpyware
ComboFix
OTL

On the other person's computer
Ad Aware
AVG
Malewarebytes' Anti-Maleware
Spybot S&D
Uniblue Speed Up My PC

I will also update whenever I receive more recommendations and cite the source (whenever applicable, certain sources I wouldn't want to advertise due to various site rules).

I use:
Malewaerbytes' Anti-Maleware
HiJackThis!
Spybot S&D

I use to use:
Avast - I no longer use this because it was slowing down my computer to the point that it was taking 20-30 min to startup...if it did not freeze. Long story short...Avast was not compatible with Windows 7 when Windows 7 first came out, so I switched to Malewarebytes.
Peer Protector - a nice ip blocker that works with windows xp, but does not work with vista nor 7 last I checked
Ad-aware - a great ani-spyware program, but after I switched to Malewarebytes, Ad-aware stopped catching things...so it seemed pointless to keep it on my computer

MBAM is antivirus also? Ah, I see (checked my own MBAM) the actual realtime protection is a purchase only function...

I used to use Spybot S&D, but I heard that SAS was better at one point, and that SpywareBlaster was better still... Any opinions on that?

As for me, I haven't had any issues with avast yet, and I run XP so yeah. IDK what OS's are running on what computers in the household, but I know the main one we're having issues with now is XP also, and since its owner didn't keep up with what programs are better, nor did he keep up with regular maintenance or updates, coupled with just leaving it... well, the computer's pretty bogged down. Hell, he leaves it on 24/7... I have no idea why though... I thought it was a good thing to shut down the computer regularly... Besides just saving power lol.

I normally only use Spybot S&D if MBAM fails to remove something, in which case I run Spybot S&D in safe mode.

Ah, alright. Know anything about these programs? The following quotes are taken from YahooAnswers. I do not recommend clicking any links posted in any quotes, as I have not investigated them personally yet.

ad aware and avg are both anti virus systems.
one or the other should be removed,
i suggest AVG is removed as it is completely useless

malwarebytes is a must have,
but it must be paid for to enable it's real-time protection.

Everything by uniblue is a total scam.

Spybot S&D is a very old and slow program,
it is of no use in the computers of today.

Check this out.
Advanced SystemCare Free : http://www.iobit.com/advancedsystemcareper.html

instead of windows firewall - Use commodo firewall [Best free firewall ]
avast! Antivirus - use avira - bettter than avast
Puran Defrag = instead use Auslogics Disk Defrag
HiJackThis! = warning double rechk bfore u do any changes
Puran Defrag = instead use Auslogics Disk Defrag
Malewaerbytes' Anti-Maleware = with free version , u should manuelly scan weekly
windows firewall = Turn off it
Windows inbuild Windows Defender(on win7/vista) = Tool menu > Turn off it (or from services.msc)