When you're designing an external optical drive, you need to keep a couple of things in mind. Being external, it needs to be relatively small; people buy external drives for portability, after all. It also needs to be reasonably robust; unlike an internal drive, an external drive is likely to undergo more knocks than average. Sony's slim DRX-S70U drive addresses both of these areas neatly. It's a slim (135.5x19x154mm) and light (440g) drive in a rigid black metal casing. As such, it should slip into most notebook bags without creating too much of a bulge -- if it weren't for the AC power adaptor and USB 2.0 cable, which expand its bag size noticeably.
The DRX-S70U is a combo DVD/CD burner with support for every format you'd care to throw into it, from humble CD to DVD+R DL. Rated write speeds are 8x (DVD+/-R), 8x (DVD+RW), 6x (DVD-RW) 4x (DVD+/- R DL) and 24x (CD/CD-RW).