Update: BioWare has announced issues with the Return to Ostagar DLC that lead to its being pulled from the Xbox Live Marketplace. More information here.
The twice-delayed Return to Ostagar DLC for Dragon Age: Origins seems to have fought its way onto Xbox Live, as reader Harry has sent in a couple images showing the item being available through the in-game menu. Going through Xbox Live, we managed to access the content after sorting by "All Downloads." We can confirm that neither the PS3 nor PC versions of Dragon Age: Origins could access the add-on at the time of writing this post.
By the way, Harry, if you need some help spending all those points you've stacked, we may have a few ideas for you.
Shortcut: Return to Ostagar for Dragon Age: Origins [Xbox.com]
Source - Return to Ostagar download screen
Source - Dragon Age: Origins menu