The current installment of DC Comics Universe, or DCU, comes out on DVD and Blu-Ray on February 4th, but apparently you can buy the digital download already.
iTunes has it at $19.99, although I have no idea what kind of features it comes with. However, Amazon Instant Video has two versions; the regular movie, and the movie with bonus features, both at $19.99 for the HD version, and $14.99 for the SD version.
I find it weird that Amazon has the download with bonus features costs the same as the one with just the movie, but that’s what it says in the listing, so I guess there’s no mistake there.
The bottom line is, if you can’t really wait to watch it, then go for the digital download, otherwise you can always pre-order the disc version.