Sinnoh Legendary Pokemon

Dialga,Diamond, or Palkia,Pearl.
Atop Mt.Coronet after obtaining the Icicle Badge. Level 47.
Uxie,Azelf,Mesprit. All Level 50.
Uxie:Acuity Cavern.
Azelf:Valor Cavern.
Mesprit :Verity Cavern, then random routes.
Heatran:Stark Mountain,Back room, 2nd visit. Level 70.
Regigigas:Put Regice,Regirock and Registeel into your party.Go to the last room in Snowpoint Temple. Level 70.
Giratina:Found at Turnback Cave, past three pillars. Level 70.
Cresselia: After obtaining the National Dex, go to Canalave City. Go to the Sailor's house, then speak to the boy and his mum. Go to the sailor. He will take to Full Moon Island, chase it like Mesprit. Level 50.
Event Pokemon:
Manaphy
From Pkmn Ranger, Level 1 from egg.
Phione
Ditto+Manaphy+in daycare= Phione eggs. Not really classified a Legendary yet, as you can get many Phione eggs.
Darkrai
Level 70,New Moon Island, Membership Pass needed.
Shaymin
Level 30, Route 224 White Rock, Oak's Letter needed.
Arceus(Original One.)
Level 80, Spear Pillar, Azure Flute/Heaven's Pipe needed.
Hope I helped you!!!