I have just created an Android app for designing digital filters.
You can design Butterworth, Chebyshev, 2nd Order Shelf, 2nd Order Parametric, DC Blocker, First-Order Lag, Exponential Averaging filters and IEC 61672-1 A-Weighting & C-Weighting filters (Class 1) with this app. The Butterworth and Chebyshev filters can be any order of your choosing.
The app will calculate the filter coefficients, save them to a text file (so that you can copy/paste the values into your code) and plot the frequency response.
Most of the filters are designed by transforming the s-domain equations to the z-domain with the Bi-linear transform and frequency warping. The DC Blocker and shelving filters are taken from the literature. For the higher order filters I have used convolution to perform polynomial expansion to merge filter sections together. The A-weighting and C-weighting filters have a frequency magnitude response that is within the tolerance of a Class 1 system as defined in IEC61672-1. All of the filter designs have been verified using Matlab.
As the readers of this newsgroup are experts in this area, any constructive criticism would be most welcome.
Take a look at https://play.google.com/store/apps/details?id=drnelly.digitalfilter