Here is a list of references that I have used over the years.

My goto reference for DSP is Oppenheim and Schafer's Discrete Time Signal Processing but for learning DSP I recommend Steven Smith's The Scientist and Engineer's Guide to Digital Signal Processing. Please see this blog entry :

As a point of historical note Park's Principles of Sigma-Delta Modulation for Analog-to-Digital Converters is a really useful reference for any narrow band signal processing applications and I have used it as a reference for wireless and ultrasound applications. If you can find a copy on the web it is well worth a read.

Analog Devices, DSP Applications Using The ADSP-2100 Family,
Prentice Hall, USA.

Antoniou, A., (1993), Digital Filters : Analysis, Design
and Applications,
McGraw-Hill, USA.

Bellanger, M.,
(1984), Digital Processing Of Signals,
Theory And Practice,
John Wiley & Sons, UK

Burrus, C.
S. and Parks, T. W., (1985), DFT/FFT and Convolution Algorithms,
Wiley Interscience, NY,
USA.

Cooley, J.W. and Tukey,
J.W., (1965), An Algorithm for the Machine
Calculation of Complex Fourier Series, Mathematics of Computation, The
American Mathematical Society, USA.

Defatta, D.
J., Lucas, J. G. and Hodgkiss, W.
S., (1988), Digital Signal Processing - A system
Design Approach,
John Wiley & Sons Inc., USA.

Higgins, R. J., (1990), Digital Signal Processing in VLSI,
Prentice-Hall, Englewood Cliffs, N.J., USA.

Harris, F.J., (1978), On The Use of Windows For Harmonic Analysis With the Discrete Fourier
Transform,
Proc. Inst. Electrical and Electronic Engineers, January.

Kay, Modern Spectral Estimation,
Prentice-Hall Inc., USA

Knuth, D. E., (1981), Seminumerical Algorithms, vol
2 of The Art of Computer Programming, Addison-Wesley, USA.

Park S., Principles of Sigma-Delta Modulation
for Analog-to-Digital
Converters (APR8.PDF), Motorola Inc., USA

Marple,

Digital
Spectral Analysis with Applications, Prentice-Hall Inc., USA

Nussbaumer H.,

Fast Fourier Transform and Convolution Algorithms

Qian, S
and Chen, D., (1996),

Joint Time-Frequency Analysis,
Prentice-Hall Inc., USA.

Oppenheim, A. V. and Schafer, R. W., (1989),

Discrete
Time Signal Processing,
Prentice-Hall Inc., USA.

Orfanidis,
Sophocles J.,

Introduction to Signal Processing,
Prentice Hall, Inc. :

http://eceweb1.rutgers.edu/~orfanidi/intro2sp/
Proakis, J. G., and Manolakis, D.
G., (1992),

Digital Signal Processing -
Principles, Algorithms and Applications (2ed), Prentice-Hall, USA.

Proakis, J.
G., Rader C. M., Ling, F. and Nikias, C. L., (1992),

Advanced Digital Signal Processing, Macmillan Inc.

Smith, Steven W.,

The Scientist and Engineer's Guide
to Digital Signal Processing :

http://www.dspguide.com
Sorensen, H. V., Jones, D. L., Heideman, M.
T. & Burrus, C.
S., (1987), and Sig. Proc., Vol ASSP-35, No Real-valued Fast Fourier Transform Algorithms,
IEEE Tran. Acoustics, Speech 6 pgs 849-863. (1981)

Stimson, G. W., (1998), Introduction To Airborne Radar (2ed), Scitech
Publishing, USA.