I-O Data offers the BRD-M2S 50GB Blu-ray burner drives in Japan with Windows Vista driver support.

The BRD-M2S comes as BRD-UM2S (photo) external drive with USB, as BRD-AM2S/BRD-AM2SB an internal drive with ATAPI connectivity.
I-O Data bundles the Ulead DVD MovieWriter5 BD Version with the Blu-ray drives. The company highlights that you can create Blu-ray video discs that you can watch on the Sony PS3, an obvious thing, but it is still early days for Blu-ray authoring.

Japanese site PC Watch Impress tested the drive with a couple of Blu-ray authoring software packages on Windows Vista. They ran into a couple issues. It looks like the whole making Blu-ray discs is still a time consuming early adopter adventure.

The external BRD-UM2S sells for 85,000 Yen (~$700) and the internal Blu-ray writer drives for 79,800 Yen (~$658).
More details on the IO Data site (Japanese).

Here in the US you can buy for instance the LiteOn Blu-ray writer on Amazon.com for 601.95 (Compare Prices).