Richard Lyons has a great DSP book. It doesn't get bogged down in the math so much as many other books do and breaks down DSP concepts very well. He has a DSP book that is mentioned by the Nuand guys and is defently worth it.. I have a digitial copy my self I use as a desk reference.
For those who are new to complex sampling and don't get how a real signal is represented in a complex plane, this essay article from by Richard Lyons is a great introduction.
http://www.ieee.li/pdf/essay/quadrature_signals.pdf