Good Starting Material for a SEMI Beginner I come from a hardware background and I am wanting to get myself more involved with the digital signal processing side of things. 

I understand a lot of concepts, but only through application meaning I don't understand a lot of the theory. 

If anyone could point me in the direction of some nice material that I could read over that can help me get a grasp on the basic material I would appreciate it!

Thanks!
Signal Processing First _ McClellan


Very readable introduction to signal processing.


Signals and Systems_Haykin


Probably the most readable undergraduate book on signals and systems.


Signals and Systems_Oppenheim


Classical text on upper undergraduate Electrical Engineering introduction to signals and systems. Not an easy read but definetely worth it. However, it's very critical to find a solutions manual for benefiting from this book.


Discrete-Time Signal Processing_Oppenheim


Formal introduction to the subject matter. Find a solutions manual.