So. To save you some time, none of them need to be read in order (although Consider Phlebas is the best starting point), the books I recommend are:

Use of Weapons, Excession, Look to Windward, Matter, Surface Detail

…. Wait. You know, I just looked at a list of the Culture novels and realized I HAVE read them all except Surface Detail(which I am currently reading and enjoy) and honestly Player of Games is the weakest of the lot followed by Hydrogen Sonata.

You really did stop reading right as it gets really good. Use of Weapons and Excession especially open up the world and really start pushing cool concepts.