Zapdos, Raikou I guess (don't really like the Beasts), Registeel, Rayquaza (Groudon's also pretty epic), Azelf, Giratina (Palkia's cool too. Dialga looks like a puppy), Thunderus-T (just LOOK AT HIM!), Terrakion (Roflstompr destroys all), Zekrom.
I'm not easily impressed; I'm usually oblivious to whatever's in front of me. Stunfisk is the epitome of monstrous majestic legendary creatures that spew fire.
Gen I birds: Zapdos Gen II beasts/gerbils: Suicune Gen III golems: Regirock Gen III weather trio: Kyogre Gen IV pixies: Azelf Gen IV creation trio: Giratina Gen V kami trio: Thundurus Gen V tao trio: Kyurem Gen V musketeer: Terrakion