My suggestion would be OWC:
http://eshop.macsales.com/shop/firewire/optical-drives/
In my experience, you probably won't see a tremendous increase in performance except for ripping DVDs. Random access of CD's & DVDs has some technical issues that cause low thoughput. In a "continuous" data stream like a DVD rip, then there would be benefit from the faster throughput of Firewire. But random access doesn't see as dramatic an improvement.
And writing DVDs, often you end up burning at a slower speed because of the quality of the blank disks or drive mechanism. (IOW, burning DVDs at 8x causes more "coasters" than burning at 2x.) So again, offsetting the speed advantages of Firewire.
So IMHO, don't expect "greatness" from a Firewire optical drive. I'm not saying don't get one, as I still think you'll see an improvement over a USB drive. Just don't be surprised if you do NOT see an improvement.