Viper Rescue Program
Scan and clean an infected computer when programs cannot be easily run.
AVG Rescue CD and the User Guide
This needs to be burned to CD but can also be used from a USB memory stick.
Avira Rescue System
To use the Rescue System burn it to a CD or copy it to a bootable USB stick and then boot your system from that CD or USB stick.
F-Secure Rescue CD
Boot up securely with the Rescue CD.
Comodo Rescue Disk
Scan your entire system for viruses before Windows loads.
Bitdefender Rescue CD
A free tool that scans and cleans your computer whenever you suspect a malware threat.