I pursued my bachelors' degree in business administration, but my interest in Information Technology led me to acquire some knowledge of PHP programming and MySQL database. I find programming so interesting that I haven't applied for any job since my graduation. Currently I am staying home and just trying to acquire in-depth knowledge of PHP programming. So far I have developed couple of websites and web applications including Inventory+ Point of Sale Software and an Accounting system for small organizations.

I aim to have knowledge that a Computer Science graduate should have, and for that I want to read books but I have no idea where to start from.

Could you please suggest me some books and topics that I should study on?

Thanks a lot :)