What kind of video camera and housing do you have? Depending on your combo it may float.. but this varies from housing to housing.
SPL Waterhousing we're primarily designed for the Surfing industry, so they come with a leash that you can attach to your wrist for added safety.
This has some pictures and details on the SPL housings: http://www.norcalsurfers.com/word/features/spl-waterhousings/
the dual video/photo housing is pretty cool!