Check this out, especially the recommended reading section.
http://www.bluebearsound.com/articles/index.htm
I got these 2 so far:
Modern Recording Techniques - Huber & Runstein
The Mixing Engineer's Handbook - Bobby Owsinski
The first is more a reference guide covering everything concerning audio. The 2nd is sort of a Q&A with a bunch of very well respected engineers. You get a lot of different approaches to various studio techniques. Highly recommend that one.
For playing keys, I got “Piano For Dummies”. Good book actually. I got “Picture Chord Encyclopedia” by Proline, which is a huge book with pretty much every chord (plus it’s inversions) and pictures. I also got “Hanon - The Virtuoso Pianist in 60 Exercises”, which is real good technique/speed builder.
Business related, I have “Kashif’s A&R Source Guide” and “The Musician’s Atlas”. Both are very good resources for industry contacts. The Atlas gives you managers, lawyers, booking agents, radio stations and clubs from around the country too.
I got a subscription to Keyboard magazine. I used to get Electronic Musician, but they’re too devoted to software now.