The third book rumoured to be called "The Victors" (it isn't officaly titled though) is said to be published worldwide in August 24th 2010.
"The much-anticipated third book in Suzanne Collins's #1 bestselling The Hunger Games trilogy will be released in English worldwide on August 24, 2010 (Untitled third book of The Hunger Games trilogy, U.S. hardcover edition ISBN: 978-0-439-02351-1, $17.99; Simultaneous release from Scholastic Audio, U.S. edition ISBN: 978-0-545-10142-4, $39.99)