Update: At this point, these will be next month's GwG. Look forward to them. :D
Original: First, this isn't 100% at the moment, so don't freak out if it ends up being different.
IDARB will continue to be free for those who haven't downloaded it, but as this IS a rumor at the moment, you may want to get it if you haven't. IDARB is an odd party spots style game that utilizes social networking, mainly Twitter, and incorporates tweets in-game.
Rayman Legend will also be free, this is the fifth game in the main series and has received critical acclaim with near perfect scores, averaging a 9/10. The lowest score this title received was an 83% (out of 100%, obviously), and that was on the VITA.
Bioshock Infinite will be free for the first half of the month. Thus is the third installment of the Bioshock series, yet taking place in another version our dimension. Infinite features Detective Booker DeWitt who's been instructed to find a mysterious girl and return get to New York.
Bioshock Infinite also received critical acclaim, receiving several perfect scores and winning many awards, including "Game of the Year" in 2013.
Tomb Raider will be free the latter half of the month. It is considered a reboot of the series (although the only one I played was the first, I think, on the Playstation), it has also received many positive reviews, averaging a respectable 8.5/10.
The game is notable for its graphic display of violence, particularly that part when she gets impaled on the tree branch in the QTE-esque river part, and offering players many ways to complete an objective.
Again, this is just "word of mouth" right now, and we'll update this when we hear verification or not.