If you're interested in testing a product across many different OS's, then you're interested in getting AWS to boot lots of different OS's.

unorthodox OS's

• there are lots of orthodox ones at:
  • cloudzoom ⇐ go there
  • amazon
  • ubuntu
  • bitnami
  • turnkeylinux
• FreeBSD
• OS/X
  • This is a little trickier, because of licensing issues. Apple REALLY prefers you use OS/X on legit hardware. But lots of people have gotten it to work on other VMs, so it should work on Amazon's VM too.
  • [1]

instructions for getting custom OS's to work on EC2

• A Process of Making a Custom HVM Virtualized AMI for EC2
• how FreeBSD was made to work on HVM [1] [2]
• Creating your own AMI for Amazon EC2

other notes

• notes on safely using Shared AMIs (more)