I would suggest against a usb cd-rw. If you have an imac, this is your only option, but I still would hold out until you upgrade to an imac with firewire ports or a g4 with firewire ports. USB is just too slow at 12 mps (megabits per second.) However firewire can go up to 800 mps. If you do get a usb cd-wr..... go with the QPS drive. It's much nicer than the sony, and comes with a great garauntee. Plus it comes with Toast, which is the only cd software that is really fantastic on the mac. (If you have one of the new imacs, you DO have firewire ports. If you have a slot-loading cd hole, you have the new imac.)
Cheers,
Bob