Since your thread got closed and I don't want to waste a long response I typed...
There's Kyurem (Ice/Dragon) in Giant Chasm, the 3 (New) Legendary Dogs, in Mistralton Cave, Pinwheel Forest, and Victory Road, and there's the roaming legendary pokemon, either Thundorus or Tornadus depending on what version you have, that begin roaming once you head to Route (6 Was it?) after the lady tells you that there's a massive storm there before you enter Route 10 to the Elite Four.
Note you can only find Cobalion at first, the others remain hidden until you catch or kill Cobalion. Cobalion is a Steel/Fighting type and is in Mistralton Cave. You need Stength, Flash, and Surf to get to it. After that, Both Terrakion and Virizion are now availiable. Virizion is in Pinwheel Forest, enter from Nacrene City side and go north until you see a path that forks right. Just look around here for a while, I can't remember precise details. Terrakion is in Victory Road, I believe you have to start from the Pokemon League side, enter the cave and take the stairs down on the left, use strength to move the boulder forward so you can enter the path left, where Terrakion is.
Hope this helps.
Oh, and there's Landorus at Abundant Shrine, but he only appears if you have both Thundorus and Tornadus in your party.