I honestly can't say enough good things about this text.
It reads really well, but is also very thorough and concise. It was written by Steven W. Smith, and get this - you can actually peruse the chapters (and yes, download them) for free.
There are some really great topics in this text that cover some pretty important and fundamental concepts in digital signal processing. As an example, here's a link to a chapter about dithering and for what type of signals it matters most (hint - it's probably not the kind of signal you're thinking of):
The main link can be found here: http://www.dspguide.com/pdfbook.htm
Again, this is one to have in your 'go-to' list of reference materials, and to be able to read it for free, well that's just an insanely-good bonus.