USB Drives & CD/DVD

For USB drives you may wish to try ForensicPC's Ultimate Write Block Kit.. For imaging, I have successfully used Helix. If you're more comfortable with Linux and command-line operations, you may wish to mount the USB drive as RO (It should show up as /dev/sda or some-such) and then run DCFLDD to image and create hashes on-the-fly.

For CD/DVD, I would think a read-only drive would well to ensure nothing is written the the subject disk.

Hi
With cds and dvds (read only memory) the easiest method is to use EnCase to image them and / or isobuster to preview them. If they are re writable, you would still require burning software to change anything on the media so by placing the cd / dvd in the drive it is still regarded as being forensically sound.

I have always used the CD and DVD Forensics book as my reference. As far as software, EnCase & FTK have somewhat limited capabilities so the afore mentioned ISOBuster or the dedicated CD/DVD Inspector are my tools of choice.

A read only CD/DVD drive is absolutely necessary on any XP, Vista or Mac forensic station as those OSes have CD burning software built-in.