The Pop Piano Book is such a thorough examination of how to become comfortable creating your own accompaniments from lead sheets in the following styles:
Pop-Rock and Hard Rock
Country & Country Rock
The author Mark Harrison starts with a comprehensive section on contemporary harmonic and rhythm concepts before launching into all the above mentioned styles. Midi files of all 800 music examples are available.
Not for the complete beginner, this is a must own book if this is your game on the keys!