the avatar portal has them all online in decent quality. http://www.theavatarportal.org/Watch-Episodes.php . for downloading, my favourite site for finding torrents is isohunt.

i'm super psyched about korra. i love the original show, but picking up again with the original characters would've been overkill, since their story is done. mike and bryan can do no wrong as far as i'm concerned, and i can't wait to hear more about it