It's worth it to get all the Blue planet series(the Box set). It is one of the best documentaries I think I've ever seen. I think it is also due to the fact they had the largest budget for a documentary. It won't make you a better reefer but the quality of the entire series is unmatched. They also did a re edit that they were going to release as a movie type feature but I have yet to see it.
There is no narrative, but CORAL SEA DREAMING is quite good for visuals only. It's close up sequences on coral spawns are fantastic.
I haven't ordered it yet, but Aliens of the sea might be worth a try.
http://www.aliensofthesea.com/
I will give you some warning, anything produced by MADACY Entertainment tends to be of poor quality. Usually no narratives and when they do have them they are poorly done. They did the sport diver series. Many of the DVD's play like a low quality training video. Save your money.
I'd say a trip to the library and browse through the national geographic documentaries would be a great and inexpensive way to see some good movies.