Unlike most people who crave for that 66% off Dark Souls, or Batman titles, I tend to use Steam Sales to try out new indie games that fly under the radar.
Last Christmas I found some AMAZING hidden gems:
So far this Summer Sale I've already found one:
Pixel Piracy (full disclosure, I love ANYTHING Pirate related without exceptions.)
List here some lesser known indie titles to look out for sales on. I highly recommend any of the above... especially Valdis Story.