Actually, here is a good summary of all the DLC reward items, as far as I could tell it's spoiler free. That being said: Leliana's Song. Origins (complete Stone Prisoner, Warden's Keep & Return to Ostagar during the playthrough.
DLC Order. This is the rough order I plan on tackling both games. Let me know if something seems off. Dragon Age: Origin Leliana's Song (Already beat it, but might do it again to get the armor) Origins Return to Ostagar (During Origins) Warden's Keep (During Origins) The Darkspawn Chronicles (After Origins) Awakening
The DLC for that game have always been wonky. I remember when I installed awakening/DLC titles, it involved doing a hard drive swap, creating a origins account, and a lot of other stupid human tricks. It took about a week until I had all of the logins in order and the additional hardware required. And in the end, two of the DLC assets did not VNnn6.