List of...

Dialga, Palkia, Azelf, Mespirit, Uxie, Giratina, Heatran, Shaymin, Darkrai, and Arceus.

Ok, here's the list and where to find them:

Dialga: At Spear Pillar (Diamond Version)

Palkia: At Spear Pillar (Pearl Version)

Uxie: Lake Acuity Cavern after killing/catching Dialga/Palkia

Azelf: Lake Valor Cavern after killing/catching Dialga/Palkia

Mesprit: Find it in the Lake Verity Cavern after killing/catching Dialga/Palkia, then find it again randomly in the grass and you can catch it. This will take luck.

Giratina: You may only obtain Giratina after defeating the Pokemon League. Go to the route right below Veilstone City - the route with all of the fences. About halfway down this route, you will notice that there is a fence around what looks like an entrance to a forest (not really a door, but an alcove in the trees). Get into the fenced-in area and enter that alcove of trees. You will find yourself on a little road called spring path. Follow Spring Path until you reach an area with a large depression in the center. In that depression there is a lake. But, more importantly, there is a cave entrance (a little black openning). Use rock climb to get into the depression from the cliff you were just on, and enter the cave. You will be in a place called Turnback Cave. At first it just looks like a sqaure room with a door on each wall. Well, it's actaully one of the most annoying caves to navigate in Pokemon history. Actually, all I did to find Giratina was enter a bunch of random doors until I found the room with Giratina. This could take a couple of minutes to a couple of hours depending on how lucky you are. Well, however long it takes, you'll find Giratina eventually. Fortunately, Turnback Cave is easy to exit - just turn back (Enter and exit the same door).

Heatran: You can find Heatran at the back of Stark Mountain. Stark Mountain is only accessable after you beat the Pokemon League. Once you enter Stark Mountain the first time, you will be greeted by a red-haired trainer named Buck. He will follow you throughout Stark Mountain until you get to the furthest back room, where he will obtain an item he was looking for called the magma stone. Then he will leave. You'll wonder: "Where's Heatran?" Well, before finding him, you're going to have to get out of Stark Mountain and enter the area at the foot of it called the Survival Area. At the upper-left house of the Survival Area, you will find Buck again. He'll talk to you, and then walk away. Now, go back to the furthest back room of Stark Mountain (where Buck found the magma stone) and you will find Heatran waiting for you. Cresselia: You can only obtain Cresselia after defeating the Pokemon League. First, go to Canalave City. Near the area with the sailor that asks you if you want to set sail, there is a house with a sign next to it. The sign says "Sailor's House," or something along those lines. Enter this house. Inside, you will find a little boy in a bed, with a woman (his mom, apparently), standing over his bed. Talk to the little boy. Apparently he is sleeping and having a bad dream. Talk to his mom. Apparently, she's awful worried about her little boy. Now, exit the house. Now that you have an idea of what's going on, talk to the sailor that asks you if you want to set sail. He'll ask you to sail with him to a place called Full Moon Island. He wants you to find an item there called the lunar wing that will apparently save his son (the little kid with bad dreams). Sail to Full Moon Island. There, you will find a room with a puddle shaped like a crescent moon, along with Cresselia. Talk to Cresselia. It will run off like Mesprit did, and it will drop the lunar wing. Get the lunar wing and sail back to Canalave City. Then, give the lunar wing to the little boy and he will awaken from his nightmare. Now, you can find Cresselia at random in the Sinnoh grass (like Mesprit).

Manaphy: You must import the special egg from Pokemon ranger to your game card in order to obtain the egg and hatch Manaphy. I forgot what the egg's proper name was, but you'll know it's the manaphy egg when you see it. It's blue in color with yellow and pink spots on it. Alternatively, you can use the Action Replay and hack a Manaphy.

Shaymin: Only available via Nintendo Events. Or, you could use Action Replay.

Darkrai: Only available via Nintendo Events. Or, you could use Action Replay. Arceus: Only available via Nintendo Events. Or, you could use Action Replay.

Ok, that's all of the Sinnoh Legendaries. Hope I helped!

Darkrai is found on Newmoon island at lv.40 and you need the Members Card to get to him.must have healed the little boy first and have NPD(national pokedex).That house in Canalave City is where he is.When you get to Newmoon island, you MAY NOT LEAVE untill you:kill darkrai,catch him,or if he kills you.Shaymin is found in Flower pardise at lv.30.you must have Oak's Letter to find her.need NPD.goto route 221 I think(one next to elite 4)at the end is oak,who tells about the rock and shaymin appears. Arsesus is at Hall of Orgin above Spear Pillar.hes at lv 80 and you need Azurel flute and NPD to find him. Go to spear pillar with flute and then up there you will be asked if you want to play the flute.when you do, a staircase will appear and take you to Hall of Orgin,where Arsesus is.hope this helps.

Here is the answer:

For sinnoh:
You got them all

For National Pokedex:
Yours, Rotom, Heatran, Regigigas, Cresselia, Phoine, Manaphy, Darkrai, Shaymin, and Arceus

Hope this helps you!!!

The rest of the legendary Pokemon include Hetran, Giratina, Regigigas, Manaphy, and Phione.

Yeah, to find the ones not yet explained:
Rotom: Not exactly sure, I know you must get it at night time in the Old Chateau.

Regigigas: Transfer the three regis to your game and then go to the temple in Snowpoint.

Cresselia: After getting the National dex, go to... Canalave City I think. The one with the port to sail to iron island. Talk to the sailor or his family, don't exactly remember which, and you will find out his son is having a nightmare. The sailor asks you to go to Fullmoon Island with him to get a feather. You will get there, Cresselia will drop a feather and fly off. Take the feather to the boy, and he will wake up. You will then have to track Cresselia like you did Mesprit. Phione: After getting Manaphy, breed it with a ditto to get a phione.

There you go. All of these answers combined will help you get Sinnoh's legendaries.

Dialga, Palkia, Azelf, Mespirit, Uxie, Giratina, Heatran, Shaymin, Darkrai, and Arceus.