I've been shopping for an external optical drive for my wife, how is getting new iMac, and will probaly go for this one:
https://eshop.macsales.com/item/OWC/MR3USD24/
Also look on Amazon.
Features about the one I linked that I like, and recommend you consider, regardless of where you shop:
- tray-load optical drives are generally more reliable than slot-load drives.
- It has its own power supply. Again reliability. Drives that have to scab all their power from the computer's USB ports are not as reliable, especially on older devices.
- It is USB 3 so it will still be relevant when you replace your 2008 with something newer. Retained value.
- The power and data cables are separately replaceable should the cat chew through one. Many of the smaller (cheaper) "mobile" optical drives have a combo power/data cable that is permanently attached. If that cable gets damaged, the cat will owe you a new drive.
The one negative only applies if you need to travel with an optical drive. The one I'm considering is heavier if there are travel weight concerns, like packing for air travel.
The above drive is about the same cost and the now-discontinued Apple USB SuperDrive.