Best book (besides rule book) for learning rules?

[kdf5]

For an in-depth look at the NFHS rules buy the Redding Guide:

Home Page

The NFHS usually has their football rules meeting in Jan/Feb so the 2009 Redding Guide should come out in May/June, somewhere in there.

You can also read through these:

Football Files

The link to Penalty Enforcement (not All But One Penalty Enforcement) is a great framework for applying most any penalty to any situation.

[ODJ]

Referee Magazine is a good source. They publish "Rules by Topic" books.
Reddings are very good for football.