Asus has recently launched an external Blu-ray drive powered solely by a humble USB cable. We sort of missed it when it came out, but decided it's worth mentioning anyway.
The ASUS SBC-04D1S-U is a rather stylish device, and the fact that you don't need an AC adapter makes it practical too. It reads Blue-ray at 4.8x speed, while DVDs can be accessed at up to 8x. Also, it ships with a program that supposedly improves USB performance, although we wouldn't speculate on the level of dubiousness of this claim.