Get Reshiram and Zekrom
I did this I while ago, so plz post a better version if I am off a bit.
Reshiram-when you beat the game, talk to the Area Keepers. One will mention getting 20 White Quills and headed to the Arcane Area. The bridge is broken now, so look for some. After you get about 20 the bridge is open(there is a quill with Scolipede and Burmy there too.) Head to the area, and go to the back. Switch to Snivy and jump near a ledge in the back. A Reshiram Dais is there, and if you have 20 quills, the shrine will take you in. Reshiram will then battle you.
Zekrom-Talk to Emboar after you beat Darkrai and save Wish Park. He'll give you the Deep Black Orb, which is how you get Zekrom. Head to the Warehouse, and Reuniclus will help by making a machine. However, the machine needs immense power from Land, Thunder, and Wind(Any ideas?). Head to the Beach, and go up to the Shrine there. Chant for Tornadus, and he'll play Chase. Then, he'll go to Reuniclus' Lab, but reminds you to get Thundurus. Head to the Iceberg Area, and find Mandibuzz. If you haven't already, give her some Everflames. She will then lift your party to Thundurus' Shrine. Repeat what you did at the beach, and Thundurus will go the the Lab, but tell you to find Landorus. Go to the Arcane Area(to get there, get 20 Quills.)and surf to the island. Chant for Landorus, and he will battle you. Beat him, and head to the Warehouse. Reunciclus and the trio will charge the machine and open the Orb. Finally, head to Wish Park, and go to Wish Palace. Above the throne is Zekrom's Dais. Use it to battle Zekrom.
BONUS-Befriend both of these dargons to free and befriend Darkrai, and be able to befriend Gothita, Gothorita, and Gothitelle.
Added by: Guest Mar 17th 2012, ID#5038