news report:http://dailypioneer.com/nation/59047-isro-flying-high-all-set-for-mars-mission.htmlis giving launch time as early hours of 26 April 2012 for RISAT-1.
SPOT-6 in August according to speeches after the C19 launch. Can't remember if he said it was on C20 or C21.
According to this article:India to ferry heaviest foreign satellite in Augustthe co-passenger with Spot-6 on PSLV C21 in August will be a Japanese microsatellite (15kg)(maybe PROITERES which has a launch mass of 15 kg?)