I just couldn't find out how to do this easily in OS-X ... so after a quick Googling I was

because it's in the Disk Manager.
Insert the CD you want to copy and then fire up Disk Manager in the applications/utilities folder. You'll see your hard drive(s) as well as a CD mounted. Select the first indented CD - not the root CD icon. This is because the root CD icon represents the device itself, the first indented one represents what's on it. When you've clicked it once, click "New Image" and set the options accordingly.
I'll get started straight away, but the remaining file will be suffixed .cdr - just change the name to .iso and you're good to go!
/p