Out of all the games, Diamond and Pearl has the most legendaries for the player to capture. Below is a list of all of them, and how they are aquired. Keep in mind that most of the Pokemon below are unavailable until you are given the National Dex. The exceptions are Uxie, Mespirit, Azelf, Dialga, and Palkia.

Also remember that Darkrai, Arceus, and Shaymin are NOT available in game, and only Darkrai is available legitly from an event in Japan. They can, however, be aquired through cheating. Manaphy is also not obtained through events in DP alone, as I will explain later.

Uxie Uxie is found inside the island on Lake Acuity. It is at Lv50.

Mespirit Once you talk to Mespirit inside the island on Lake Verity, you will see it's picture and then it will take off. You can find it in the grasses of mainland Sinnoh. Use the map feature of the Poketch to track it. It is at Lv50.

Azelf Azelf is found inside the island on Lake Valor. It is at Lv50.

Dialga Dialga is found at the peak of Mt. Coronet (You can't avoid it). It is at Lv47. Diamond Only

Palkia Palkia is found at the peak of Mt. Coronet (You can't avoid it). It is at Lv47. Pearl Only

Heatran Heatran is found at the back of Stark Mountain. The first time you reach its room it will not be there. Go back to the trainers house with whome you had just partnered up with. Then return to find Heatran. It is at Lv70.

Regigigas Regigigas is located at the bottom of Snowpoint Temple. You will be allowed inside once you have the National Dex and Regice, Regirock, and Registeel in your party. It is at Lv.70

Giratina Giratina seams to be the third of the trinity that includes Dialga and Palkia. After you get the National Dex, a new are will open up on the east side of Route 214. Travel along the path, enter the cave, and try to get to the bottom. Giratina is at Lv70.

Cresselia Talk to the sailor in Canaclave city (the one that took you to Iron Island). After a few lines of dialog, he will take you to Full Moon Island. When you talk to Cresselia, it will take off just like Mespirit did. It is also at the same level, Lv50.

Phione Phione is obtained by breeding Manaphy with a Ditto. It is exactly the same as Manaphy, except that it's base stats are 20 points lower in every stat.

Manaphy After you beat the game and complete the mission in Pokemon Ranger, you will be given a Manaphy egg. If you have a Diamond or Pearl game card, connect the two games (DP and Ranger) wirelessly and beggin the transfer process. Manaphy will hatch from the egg just like any other egg, it is at Lv1.

Darkrai When you obtain the Membership Pass from a Nintendo Event, go to the motel in Canaclave that used to be locked; it isn't now. When you take a nap in the bed there you will have a nightmare about Darkrai. Wake up and pick up the Diary. Take it to the sailor (The one who helped you with Cresselia and Iron Island) and he will take you to Darkrai's island. It is at Lv40.

Shaymin When you obtain Oak's Letter from a Nintendo Event, go to the white rock on Route 224. The route has now been extended. Follow it up to the top where you will meet Shaymin. It is at Lv30.

Arceus When you obtain the Heaven's Pipe from a Nintendo Event, go back to Mt. Coronet, where you battled Dialga/Palkia. Use the Heaven's Pipe and some stairs will appear. At the top of the stairs is Arceus at Lv80.