here is a nice list that is easy to understand
Capacity
Blu-Ray
ROM single layer: 23.3 / 25GB
ROM dual layer: 46.6 / 50GB
RW single layer: 23.3 / 25 / 27GB
RW dual layer: 46.6 / 50 / 54GB
Highest test: 100GB
Theoretical limit: 200GB
HD DVD
Single layer: 15GB
Dual layer: 30GB
RW single layer: —
RW dual layer: —
Highest test: 45GB
Theoretical limit: 60GB
Codecs
Blu-Ray
MPEG-2
Microsoft Video Codec 1 (aka VC1, WMV HD, etc.)
H.264 / MPEG-4 AVC MPEG-2
HD DVD
Microsoft Video Codec 1 (aka VC1, WMV HD, etc.)
H.264 / MPEG-4 AVC
Studios (movie and game) listed as supporting members
Blu-Ray
20th Century Fox
Buena Vista Home Entertainment
Electronic Arts
MGM Studios
Paramount Pictures
Sony Pictures Entertainment
The Walt Disney Company
Vivendi Universal Games
Warner Bros.
HD DVD
Buena Vista Home Entertainment
New Line Cinema
Paramount Pictures
The Walt Disney Company
Universal Studios
Warner Bros.
Format founders
Blu-Ray HD DVD
Sony Corporation
Royal Philips Electronics
Toshiba Corporation
Hitachi Corporation