Free programs to perform boot-time virus, spyware, malware scanning?

I would like to know of any free programs that will allow me to perform a boot-time scan for viruses, trojans, spyware, etc. I know that avast! Anti-Virus has this feature but I like having options. If the program must be installed in order to perform the scan, that is fine. Any boot disks or rescue disks would meet my requirements as well. Thank you in advance for any help that you can provide.

You already know the truth Man! The immortal truth, enshrined for all time in the minds of all computer geeks in their quest for perfection – at no cost to themselves of course! The truth that IS Avast! Free Edition! So why confuse yourself Boy? Why tax what little grey matter you are actually not currently using for greater things? Download, install, live well and prosper!

Disk Rescue 2009-2010 full version

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System Suite 9 Professional $3.95 All-in-One PC Tune-Up Repair and SecurityProduct Information[For Use on Up to 3 PCs - One Year Subscription]System Suite 9 Professional (3-User) keeps your PC safe healthy and error-free providing you with everything you need to fix speed up and protect your PC.  The System Suite’s easy-to-use interface lets you remove viruses and spyware diagnose and fix Windows problems clean hard drive clutter…