What kind of theory level are you talking, balstingas10?
There are many kinds of books, so consider level, instrument, and purpose at least.
Level can be beginner, intermediate, advance, and then something like.. the 20th century stuff where composers are still making up rules and all.
Instrument can matter. For example, a guitar teacher teaching guitar theory will approach the subject differently than would a flute teacher teaching flute theory. If you're not learning a specific instrument (or many), then piano theory is a safe bet, since everything is based on the musical keyboard's layout, and it's easy to make chords, play scales, and all that.
Purpose is also a defining factor. Do you want to be a composer? You'll have to know a lot of theory. If you want to learn drums, then you might not need scales or chords, as the drums doesn't have a way to really play a traditional scale or chord.
So anyway, can you narrow it down before we recommend something your way?
Thanks!