What to read depends what you are wanting to understand.
However, "Scripts people Live" Claude Steiner, "Born to Win" James and Jongway are some of the books that followed "Games People Play" and I got a better understanding from these books.
I would have a good look around the net before you get more books. That way you know if you they come close to giving you what you are looking for.
TA Tutor.Com has some good resources, there are so many good books out there. All mine are very much out of date and unless you are wanting to really get into studying read what helps you understand things.
Words of caution :-) no book or psychological model is ever likely to give us all the answers. People are, for the most part, just trying to get through life the best way they can.
We are just trying to get through life the best way we can and yes you can see "Games" being played, "The Drama Triangle" being gone round and the "Parent, Adult Child" in action, "Racket Systems" working and so on.
Learning can help make your life better and the lives around you better, understanding what you've learnt is one thing being able to use what you've learnt isn't always easy.
Good Luck and may you enjoy your reading.