So much awesome work in one thread. Couple of specific comments:
3 (Leona) - Very morning/dawn-like feel, working as intended.
8 (Vladimir) - "Evil" is the only word that can describe this - might be more suited to Veigar but there's not much in it.
10 (Zilean) - Fits the champion well; a lot of this one reminds me of a soundtrack from Final Fantasy 7, set deep underground in a magical cave - any inspiration from this series?
And a few further champions whose themes could be interesting:
Shaco - theme for a jester; make the song keep taking unexpected turns.
Anivia - think of an icy crystal cave; echoey sounds with some high-pitched stuff should work well.
Amumu - something with a vaguely Egyptian feel that makes you want to cry, I guess.
Nocturne - daaaaaarknessssss. How about a soundtrack that might accompany a nightmare...
Keep up the great work!