La Vita è Bella

If you prefer DMG or CDR format, then you can just use Disk Utilities to make image of your disks. But if you prefer ISO format, then this is the way.

1. Insert your disk into your driver, of course.
2. Unmount it but didn't eject it. To do so, you need to type this command in your Terminal: "sudo umount /dev/disk1". "disk1" may vary depends on your other drivers.
3. Use dd to create the image: "dd if=/dev/disk1 of=/path/to/foo.iso". Again, "disk1" may vary.
4. When it's done, you've got the ISO image file, and you may eject the disk now. But as a bug in Finder, you can't eject a volume which you unmounted in Terminal in normal ways. Instead, you need to type this command in Terminal to eject it: "sudo diskutil eject /dev/disk1"

The Finder bug is really annoying, even a logout can't eject the disk, you must reboot your machine. But fortunately I've found the workaround on macosxhints.