By William Gallagher BBC News Online

Naomi Watts plays a lead role in 21 Grams

One mesmerising fact - that we each lose 21 grams the instant we die - is at the heart of powerful drama 21 Grams, possibly September's best DVD.

Not for extras - there's one good Making Of - and not for obviously great picture quality as the film is deliberately quite grainy.

But it's the story and the acting from headline stars Sean Penn, Naomi Watts and Benicio Del Toro that makes this.

One terrible accident slams three people into conflict in this drama from the director of Amores Perros.

It's a consciously disjointed picture that some find hard to get in to but it's worth the effort. Watch for the supporting cast, too: Melissa Leo proves to be thoroughly underrated.

The Untouchables

This Brian de Palma and Kevin Costner mobster classic gets the special edition treatment for its DVD release.

Kevin Costner's character is out to bring down gangster Al Capone

There's an hour of extras on the making of the film with emphasis on its epic scale.

Brian de Palma proves to be quiet but informative; willing to admit he was looking to a direct a film that would make some money for once.

He did well. The famous tale of Elliot Ness and Al Capone is very well told.

It looks gorgeous: the transfer to DVD living up to how the film has the slightly sepia tone of a Western.

Dad's Army: Series 1 and 2

We've had Best Of collections but if you collect TV DVDs, you want season sets and now we're getting them - or at least, as close as the BBC can do.

Series 1 from 1968 is complete: it looks grainy and old but it's all six episodes and nearly four decades later they are still funny.

But thanks to the BBC's wiping of tapes, series 2 may never be seen again in all its glory.

We get the three surviving TV episodes plus audio-only versions of the rest.

Those audio versions are not just the sound from the TV show, they are ones that were re-recorded for radio at the time.