Was creating some ISO disc images this week with OS X Lion (from existing discs) and thought I would document the process.

Making an ISO

Using Disk Utility:

Start Disk Utility
Insert the disc you want to create an image from
Select the disc in the sidebar of Disk Utility (in my case, I selected the volume itself and not the drive)
Choose File->New Disk Image From ‘VolumeNameHere’
Select DVD/CD master from the Image Format dropdown
Click Save and wait
Finally, rename the .cdr file that’s produced to .iso.
Done!