Mathworks Filter design help
http://www.mathworks.com/access/helpdesk/help/toolbox/filterdesign/start_pa.shtml
http://www.mathworks.com/access/helpdesk/help/techdoc/relnotes/filter.shtml
http://www.mathworks.com/access/helpdesk/help/toolbox/signal/filterd3.shtml
http://www.mathworks.ch/access/helpdesk/help/toolbox/commblks/tutor211.shtml
http://www.mathworks.com/access/helpdesk/help/toolbox/signal/fdtool.shtml
Digital filter Design (FIR & IIR) non-MATLAB
http://www.s2.chalmers.se/~irenegu/dsp00_03.pdf
Textbook: Structure and interpretation of signals and systems
http://ptolemy.eecs.berkeley.edu/~eal/eecs20/supplements/master.pdf
http://ptolemy.eecs.berkeley.edu/~eal/eecs20/week14/lab.pdf
Carnegie-Mellon (Frequency Transform Table)
http://www.ece.cmu.edu/~ee551/Handouts/ee551.3.1-25.pdf
Signal representation (Chirp-Z)
http://www.ecn.purdue.edu/ECN/FAQ/applications/matlab/matlab.tutorials/slides.pdf
Quantized Filtering Toolbox ( now called Filter Design Toolbox)
http://uw.physics.wisc.edu/~nextroom/matlab_help/pdf_doc/qfilter/quantized.pdf
MATLAB IIR filter design example using impulse invariance design
http://www.coe.uncc.edu/~tpweldon/courses/eegr4124/matlab/matlab.html
Interactive filter design (non-MATLAB)
http://www-users.cs.york.ac.uk/~fisher/mkfilter/
http://dolphin.wmin.ac.uk/filter_design.html
MATLAB examples
http://www.siglab.ece.umr.edu/ee341/dsp/filters/fir1.html
http://www.brad.ac.uk/msceqi/modules/dpa/Chapter14.pdf
Window, Frequency Sampling, and Optimal
http://www.image.cityu.edu.hk/course/ee2235/notes/fir.pdf
http://cil.eecs.uic.edu/~dliu/DSP/fir.html
C & assembler
http://www.eng.iastate.edu/ee424/labs/FIRfilter/
Digital Filtering Lab (butterworth filtering white noise)
http://fubini.swarthmore.edu/~ceverba1/Filtering.html
MATLAB & C
http://www.eng.iastate.edu/ee424/labs/IIRfilter/IIR_Filter_Lab.pdf
MATLAB exmaples
http://www.siglab.ece.umr.edu/ee341/dsp/filters/iir1.html
IIR Filter Design
http://www.utexas.edu/cc/math/Matlab/Manual/faq.html#6.1.
IIR Filters (incl. pole-zero method)
http://www.brad.ac.uk/msceqi/modules/dpa/Chapter15.pdf
Analog-to-Digital Filter Transoformation (Impulse invariance and bilinear)
http://www.image.cityu.edu.hk/course/ee2235/notes/iir2.pdf
Non-MATLB (bilinear only)
http://cil.eecs.uic.edu/~dliu/DSP/iir.html
FIR and IIR Filter Design Algorithms
http://www-dsp.rice.edu/software/RU-FILTER/index.html
Concepts
http://www.bme.unc.edu/~clucas/BME99_121_C8CN.html