Some people here have mentioned The Zen of Poker. I also recommend The Tao of Poker, by the same author.

The best suggestion I have for eliminating ego while playing poker is to change the focus from the other players to yourself. Don't think of the game as one in which you must beat others, but rather a challenge of self to see if you can play the most perfect game your abilities allow.

Look at each hand as a series of decisions. Your opponents are nothing more than tips and guideposts in this decision making process. Don't read your opponent, read his actions and history. It isn't about him. It's about you.

Most importantly you need to get in tune with what your inner voice tells you to do. How many times have you called a bet or unwisely bluffed into a strong hand when you just KNEW that this was the incorrect play? A lot, I bet. Me, too. We all do it. This is because your focus has shifted to something other than making the correct decision at every step of the process. Identify where you have strayed (anger, impatience, hubris) and make the necessary mental adjustment.

Hope this helps.