Saw this on...I think Netflix a while ago, they since removed it. Saw it in a double pack with Superman/Batman Apocalypse at Wal-Mart for only 10 dollars so I picked it up. Definitely a good movie and really holds up. Also one of the best animated ones.
(Note: Also picked up a triple pack of Gotham Knight, Batman: Under the Red Hood, and Batman: Year One for 15 dollars, if anyone is interested in a deal. Note: secondary "special feature" discs aren't included, though, so you don't get the DCUA shorts (Catwoman, etc.) or the extra episodes from the DCAU shows. Still, though, pretty cheap, especially if you already own all the seasons of those shows and just buy the DC Showcase DVD which has all those shorts in it).