Riot Games has updated the 10 free Champions for this week in League of Legends, and it includes a few Champions that are free for the first time. Here's the list:

Ashe (Ranged DPS), DrMundo (Melee DPS), Evelynn (Melee DPS), Janna (Mage), Karthus (Mage), Kayle (Tank), Singed (Tank), Sivir (Ranged DPS), Warwick (Melee DPS), Zilean (Support)

More information, including stats and a look at past lineups, can be found in this thread on the official forums.