1. Awakening (yeah technically this is DLC that's also available in disk form.) Full sized 15-20 hour expansion for Dragon Age. Takes place right after the events of Origins. You can import your Origins character if they survived (preferred option) or you can bring in a kinda blank standard Warden from Orlais. You get a whole new cast of characters to fight with, although there are 3-4 that make at least an appearance, and maybe more, from Origins.
Best choice is to get the disk as it's a physical media, it's more likely to go on sale. All the final patches for Dragon Age and its DLC have come out so everything is as fixed as its going to be. 8 achievements for 250g (requires at least 2 playthroughs to get all 8 achievements as 1 is end-of-game decision based.)
2. Warden's Keep
If you play DA at all, you'll start learning the pain of destroying loot because your backpack is full. You can buy more backpack space from certain vendors (6 are available throughout the game for about 6 gold each) but you'll want somewhere to store really powerful stuff you can get early on that you can't wear yet.
That's where this comes in. Once you beat it you get a chest with unlimited space you can store whatever you want in there. You can also get a really good warrior armor set if certain conditions are met, and you can get the most powerful sword (either one-handed or two-handed) in the game forged by the new armorsmith who appears there after completion if you got the Superman inspired meteor rock from a random encounter while traveling between areas.
$7 MSRP for 50g, storage chest, new vendors, ability to unlock the strongest sword in the game and a decent armor set for warriors (25g of that 50g is an optional moral choice near the end of the DLC.)
3. (tie) The Stone Prisoner and Leiliana's Song
This is a tie because while Leiliana's Song is the best of the DLC that's not Awakening, The Stone Prisoner is where you can get the golem Shale, who can be the best tank warrior in the game and might be needed if you're playing as a rogue or Mage so you have a 2nd warrior (and gives you options if you don't like one of the other 3 warriors or you miss the one that's missable.)
Stone Prisoner was free in all new copies of Dragon Age, but costs $15 if you bought used. Shale isn't worth $15 IMO as this DLC is one of the shorter ones.
Leiliana's Song is an awesome one IMO. You play as Leiliana as she tells her backstory of running with lover and Orlesian bard mentor Margelline. About 5-6 hours long and has pretty good pacing throughout. If you search around carefully, you'll find 6 pieces of a special leather armor that is the best rogue leather armor in the game and it will work in Origins or Awakening. I would even advise playing Leiliana's Song either to start or soon after starting up Origins and it does an awesome job on telling Leiliana's backstory (something I wish they would have explored with other characters instead of what we got with Golems and Darkspawn Chronicles) and that leather armor will be used by your primary Rogue throughout Origins and quite a bit into Awakening.
Tip on the armor: You should have 5 pieces by the time you wake up in the Chantry after busting out of prison and meet the Orlesian chantry mother who is the one who converts Leiliana to the Chantry. DO NOT LEAVE THE CHANTRY. The sixth piece of the armor is in the desk behind where you wake up.
Stone Prisoner free (new copy) or $15 for new character and 50g (25 when you beat it, 25 if you complete Shale's personal quest)
Leiliana's Song $7 MSRP for 100g and the possibility of getting the best rogue leather armor in Origins (25g just for beating it, 50g for getting the armor, and 25g for an optional quest near the beginning that's REALLY easy to miss/mess up.)
5. Return to Ostagar
This was the first DLC to be released post-release as Stone Prisoner and Warden's Keep were available at launch (Bioware says it's because EA delayed the game from a summer to fall release.) It had tons of bugs and had to be taken down once or twice but it's up and running now.
One of the major events at the beginning of the game, no matter which origin story you choose, are the events that lead (not through your actions) to the fall of Ostagar and King Cailan. In this DLC, you find another survivor who gives you a key that Cailan wanted the Grey Wardens to have if he were to fall.
This is the shortest DLC and is kinda throwaway. Not much voice work and just fights with some darkspawn as you search for King Cailan's armor and documents. In addition to Cailan's armor/shield/sword (really good Warrior set) you also get Duncan's Sword and Dagger, great for any Rogue.
$5 MSRP for 25g (just beat it to get the 1 achievement,) great Warrior sword/shield/armor, great Rogue weapon set
6. Witch Hunt
This was the last DLC and came out the same day as Shadow Broker for Mass Effect 2. You can definately tell more work was put into Shadow Broker as while that was at the top of the DLC food chain (high praise by most media and up for an award on my podcast) Witch Hunt didn't have the same polish. In fact a patch had to be put out immediately after release because the game didn't properly save the "choice" you made at the end of it and didn't at times recognize the choice you made at the end of Origins.
You have your Warden and your Mabari warhound going back to Flemeth's hut looking for clues as to where Morrigan has gone. You encounter a Dalish female warrior who is tracking Morrigan after she contacted the Dalish clan from the Dalish Warden origin about the "mirror" (regardless of the Origin story you choose for Origins, the events of the other Origins still take place, just without your influence.) Your investigation leads back to the Tower of Magi, where an expert on these artifacts joins you. Apparently these are ancient portals used by a forgotten race that transport to the different dimension these creatures came from.
You track down the location of the last active portal and after beating its guardian you find Morrigan. She has already given birth and the child is already in the other dimension with her about to join it. You then have a conversation with Morrigan that leads to 1 of 3 conclusions. That choice is then saved and Bioware has promised will be part of what affects the universe of Dragon Age (see similar things Mass Effect 1 did with 2) but the extent is unknown.
Worth playing if you want to sum up the one lose end from Origins and properly set things up for DA 2 and beyond.
$7 MSRP with 3 25p achievements (you should get all 3 with a playthrough but 1 of them is sort of misable if you just zoom through the next-to-last area without searching.)
7. Golems of Argammark
Much like Darkspawn the only reason I got this is when it went on sale last time for $2.50 and I wanted to get the missing achievements. I haven't played it yet as the dwarf areas/mythology was my least favorite thing in Origins, and sludging through those areas again (all the DLC share artwork or flat out take place in the same places as Origins) is not top on my priority list.
The story is you're sent a letter from a dwarf requesting aid for a mission that seems impossible. You are to track down an entire group of Dwarves that went to research a Thaig for info about the golems (not knowing those mysteries were solved by you) that was just recently rediscovered. In addition to the darkspawn that fill the tunnels of the Dwarven empire, you discover an ancient secret that could be far worse ...
Needless to say this is the HARDEST thing to do in all of Dragon Age. Those who played the game on casual originally (like me) will be in for a shock from what I've read. Not to mention to get all of the achievements, you have to be it on hard or nightmare, which is VERY hard to take down the final boss on any difficulty, let alone the hardest difficulties of the game.
$5 MSRP for 3 achievements (1 for beating it, 1 for beating it on hard/nightmare, and 1 you should get if you explore all the areas properly and find all the research notes.)
8. The Darkspawn Chronicles
Like Leiliana's Song this is seperate from the main game and is a what-if scenario. Your usual main character dies during the Joining (not seen in the DLC but shown in the trailer for it) and now Allistair commands the Grey Wardens instead of "you." You control the darkspawn in an alternate version of the final fight from Origins and command them to take down Denerim and in turn conquer Ferelden for the Archdemon.
I don't really like the concept for this DLC and it's throwaway in terms of the story. I only bought it when it went on sale last time. DO NOT PLAY this before you beat Origins if you don't want the events of the finale spoiled. Even though it's a bit opposite since you're commanding the Darkspawn the cutscenes are VERY similar. All you only get for playing this is a sword that will work in Origins or Awakening, but it's just not worth it IMO. There's much better stuff out there.
$5 MSRP for 75g (25 for beating it, 50 for two optional, tougher objectives) and a sword
I would HIGHLY advise doing Warden's Keep, Stone Prisoner, and Return to Ostagar once the events in Lothering pass and the game opens up for you. With Warden's Keep being at the top of the priority list (unless you do Leiliana's Song before you start the main game.)
Then of course Awakening is next, and by the time you complete that your character should be around level 32-34 (cap is 35.) Next do Golems and Darkspawn if you want but I would definately play Witch Hunt pending its price as the "choice" made at the end of that has potential to affect DA 2 and beyond.