This probably isn't going to surprise anyone, as THQ has talked about sequels to both games in the past, but Red Faction 4 and Saints Row 3 are both currently in production over at THQ. Word of games comes from the LinkedIn profile of an ex-THQ product manager.
Red Faction: Guerilla ended up being a bit of a surprise hit earlier this summer, received extremely well both critically and commercially. THQ is currently planning a 'Come back to Mars' event, encouraging players to hop online for 4 times the regular experience.
Saints Row has also become a bit of cult hit, competiting against Rockstar's Grand Theft Auto franchise. Whispers seem to indicate that the next Saints Row will be a complete overhaul of the franchise, reinventing and revitalizing itself. Hopefully, with the next iteration, the series can finally step out of Grand Theft Auto's shadow.
Saints Row has tentatively been dated for the 2010-2011 fiscal year, while no date has been specified for the next Red Faction title.