According to Sony, last month's PS+ Instant Game initiative was a "resounding success." As a result, all of you PS+ members out there can add three more games to the fire: Gotham City Imposters, Pac-Man Championship Edition DX, and Renegade Ops.
This explains why two of the above titles that were initially reported by IGN as being included in the Summer Sale mysteriously never showed up. Provided that you're a PS+ member, you can nab them for free now, which is a considerable upgrade from 50% off.
Personally, I'm very happy with PS+, having been a member for over a year. I'm also happy with Xbox Live on the whole, but hopefully Microsoft will be pressured into something similar in the future -- more free games is always a good thing!