The ones you are interested in?
None of the games on sale "should" be in your collection, ARMA II for example, great game but if you aren't really into SIMs and heavy team play, you won't get anything out of it at all.
Just go through the games on sale and anything that catches your eye, watch a youtube video on it.
Don't waste money expecting other peoples opinions of games to coincide with your own, there are only ever so many games on sale at a time anyway so it's not like you'll be spending hours looking through them.