yes, you can! .... well, on black 2, if that's what you mean... :3 here are the ones i know of and where to get them (black 2/white 2 only - you can't get these on black 1/white 1):
heatran-reversal mountain
latios(black 2)-dream yard
latias(white 2)-dream yard
cresselia(black 2)-marvelous bridge (lunar wing required)
darkrai(white 2)-marvelous bride (respective item required-i don't know what it is but you need it)
zekrom(black 2, white)-dragonspiral tower
reshiram(white 2, black)-dragonspiral tower
kyruem-giant chasm
white kyruem-anywhere (dna splicers, kyruem and reshiram in party required)
black kyruem-anywhere (dna spliders, kyruem and zekrom in party required)
azelf-route 23
uxie-nacrene museum
mesprit-celestial tower
You cannot breed Legendary Pokemon without cheats, except for Manaphy with Ditto.
You can't catch shiny legendary Pokemon without cheats... sorry
Moltres, Zapdos, Articuno, Raikou/Suicune/Entei.
Don't cheat and use Poké Balls!
you cant get every legendary of Pokemon without cheats or migrating and trading with people
Im afraid you cant without cheats or hacks :( no legendary Pokemon is breedable.
Trading, Migrating, Catching the legit legendary Pokemon in pearl, etc.
I think you can catch 6 The Pokemon you can catch without cheats are: Palkia Girantina Cresselia Uxie Azelf Mesprit Heatran Rotom I forget the rest, but I know there's more!
four without cheats Articuno Zapdos Moltres Mewtwo plus one of the legendary dogs; entei, suicune or raikou
migrate them from other games or trade with someone u might know
Without cheats or any events they are Moltres Articuno Zapdos And Mewtwo
no