Latios(Latias in Heartgold), Suicine, Riakou, Enti, Ho-oh, Lugia, Moltres, Articuno, Zapados
There is probably more but I haven't discovered them yet!
;)
You can't catch any legendarys in Iron Island.
You can catch Lugia, and evolve Growlithe into Aracanine, which is not considered legendary, but literally has the title of Legendary Pokemon. Hope this helps!
catch legendarys
You can catch Rayquaza in your house upstairs after you catch all the legendarys in the game.
you keep playing...
You cannot catch both legendaries with a single game.
Currently, there is no way to get a official Celebi outside of Japan. However it may be possible to capture Celebi in future events.
You complete your pokedex and catch the legendarys
Master Balls, obviouslt
You can catch Groudon, Kyogre, Rayquaza, Regirock, Registeel, Regiice, Mew, Latios or Latias (you get to choose) and Deoxys (only though special events)! You can only catch these Pokémon after you've defeated the Elite Four and the Hoenn League Champion!
in Pokemon silver you can catch Pokemon as how you catch in other versions. in the Silver version is where the use of special Poke balls were introduced just like Fast Ball, Heavy Ball and Lure Ball.
only in WI-FI events