These are made up by me:
Articuno - Quetzal of Ice (Search for it on Wikipedia)
Zapdos - Storming Quetzacoatl (Yes, similar to Articuno, but Quetzacoatl as in the Aztec god)
Moltres - Phoenix of Fire
Mewtwo - Godly Clone
Mew - Ancestral One
Entei - King of Fire
Suicune - Water Master, or if you like the movies, The Northern Wind
Raikou - Thunder Lord
Ho-oh - Lord of Lords (Since he is the leader of the legendary dogs)
Lugia - Guardian of the Deep
Celebi - ??? Can't think of one ???
Regice - King of Ice (Taken directly from name meaning, Regi - King)
Regirock - King of Stone
Registeel - King of Steel
Latios - Eon Guardian (Same as Latias)
Latias - Eon Guardian (Same as Latios)
Kyogre - Creator of Sea
Groudon - Creator of Land
Rayquaza - Creator of Sky
Jirachi - Millenium Star
Deoxys - Space Virus
Azelf - Being of Willpower
Mesprit - Being of Emotion
Uxie - Being of Knowlege
Dialga - Creator of Time
Palkia - Creator of Space
Heatran - ??? Can't think of one ???
Regigigas - King of Giants
Giratina - Creator of Dimentions
Cresselia - Bringer of Dreams
Phione - Well, Phione's not eactly legendary, but the offspring of a legendary
Manaphy - Prince of the Sea
Darkrai - Bringer of Nightmares
Shaymin - Protector of Nature (Shaymin = Shaman, Shaman - Protector of Nature)
Arceus - The Original One
They aren't the best, but that's what I refer to them by.