The Playstation Store offers Playstation Plus members a selection of game downloads for free, as listed below. The deals:
Mercenary Kings for PlayStation 4 for free ($20 off)
Batman: Arkham City for Playstation 3 for free (pictured; low by $17)
Stealth Inc.: A Clone in the Dark for Playstation 3 for free ($10 off)
Castle of Illusion for Playstation 3 for free ($15 off)
Velocity Ultra for Playstation Vita for free ($7 off)
PixelJunk Monsters HD for Playstation Vita for free ($15 off)
Note that some of these freebies are not active yet, but should be available soon.
Before you spend another dollar on items and services like these, check with your public library. You will likely be surprised by what it offers for free.