I'd recommend getting an internal IDE drive, then getting an firewire enclosure for it. It would give you the ultimate flexibility to either make it internal or external. Of course, this is all that many of the externals are anyway. You may also want to do the same with a hard drive so you can store your most common burns if you become a seeder of any sort. I've found that my second IDE channel is slow as molasses, so I do all my burns from a firewire-enclosed IDE drive to the internal IDE on my primary channel. I think I've had maybe one buffer underrun, and that was due to taxing my CPU on other processes at the same time I was burning.

I do not have a dual-layer (DL) burner (yet), but I'd recommend one, given that they're pretty inexpensive and the price of DL media is only dropping. In a year you'll be glad you did this.