Playstation Plus has a lot of awesome stuff prepared for May, with choices ranging from classics to brand new titles. The most notable addition this month is free Awesomenauts. I can also personally vouch for Trine 2, Rock of Ages, and Castlevania: SoTN/Chronicles -- they're all quality titles. Free Awesomenauts in particular is an amazing addition, as it guarantees the initial success of the game's PS3 online community.
Rock of Ages in particular is grossly underrated considering how fun and unique it is. Either way, all this junk is free, so just grab it all! Even if you don't have the HDD space, simply "buy" the free game and it will be available on your account (as long as you have Playstation Plus). Other additions include a 20% discount for Saints Row 3, and a PixelJunk 4AM beta.