As of Tuesday, February 26th, Dawnguard is available to PS3 users in North America. Just like the first two DLCs - Dragonborn and Hearthfire - Dawnguard is on sale for 50% off ($9.99) during it's first week of availability. There's not going to be a better time to buy if you're planning on it!
The following have also been released today...
- French versions of Dragonborn, Hearthfire, and Dawnguard released in Canada
- Spanish versions of Dragonborn, Hearthfire, and Dawnguard released in Latin American markets.
Tomorrow afternoon, the French, Italian, German, and Spanish markets will get all of the DLC (available in all supported languages).