My hope is to find ones that are extremely easy to use, even for your grandma, so that we can give them to customers of FreeGeek and they can do the spyware-removal themselves.

boot USB / CD	size	signatures updated on release ISO	signatures can be updated via internet?	ease of use for your grandma
Avira AntiVir — "Rescue System"	80mb	daily	easily updated via GUI
Dr.Web — "LiveDisk"	140mb	daily
Bit Defender — "Rescue CD"	320mb	every few months	automatically during boot
F-Secure — "Rescue CD"	120mb	every few years?	automatically during boot

Ease of use

• Avira
  • downsides: the boot menu is intimidating/confusing for new users; it always boots up in German (though it's easy to switch to English)
  • upsides: once it gets past the boot menu, it's very easy to use
• AVG
  • downsides: text menus throughout; the boot menu is intimidating/confusing for new users
  • upsides: if you choose the default menu selection every time, it takes you to the virus scanner
• BitDefender
  • Very easy to use. Graphical and everything.
• F-Secure
  • It doesn't have a graphical UI like BitDefender, but it's still very straightforward.

Others

• CDs that contain several different anti-virus programs
  • Shardana Antivirus Rescue Disk Utility (Sardu) (article)
  • Trinity Rescue Kit contains four different anti-virus programs: Avast, AVG, Clamav, Vexira
    • Check Wikipedia for the latest release date. If the release date is old, you can manually update the virus signatures.
  • Ultimate Boot CD contains McAfee and F-Prot... just be sure to update the virus definitions
• not so easy to use?
  • Kaspersky has a PE builder
• more
• more