Sony started to ship the 50GB Dual Layer Recordable Blu-ray Disc. You can record once on this media. The rewritable Blu-ray disc is expected later this year from Sony.

You can record more than 4 hours of HD quality video, at a 24 Mbps transfer rate onto the 50GB disc.
Sony’s AccuCORE technology has been re-engineered for Blu-ray Disc media, with its major benefits including scratch guard, archival reliability to prevent data/image corruption and deterioration, stable writing that reduces fluctuation as the disc spins, and temperature durability to prevent warping during severe changes in temperature and humidity. Sony’s 50GB BD-R DL disc has a suggested retail price of around $48.
More details in this Sony press-release. Shop for Sony Blu-ray recordable media.