"Zelda's Secret Ocarina" was once the best place to go for this sort of thing. Tons of screenshots from the beta progress like that. This is the first time I've seen a video that many of those screenshots came from, though. Cool stuff! They've also managed to hack into the OoT debug rom enough to access some of those areas and enemies. See http://tcrf.net/The_Legend_of_Zelda:_Ocarina_of_Time_%28Debug_version%29 for info on that.
Fun fact: OoT started out by using the Mario64 core engine, but by the time the game was finished, it was so different that it might as well have been a completely different code base to begin with.
