I work for Okika Technologies producing a programmable analog device called DynAMx. Its like an analog version of a digital FPGA.
One of the things DynAMx is good at is making a configurable audio device. One of the interesting features of the tools is a filter designer. You can see the tools at DynAMx Design Lab. They are free to download at Downloads.
We are thinking of doing an Arduino shield that allows users to adjust the filter parameters and generate lots of audio effects. I wanted to ask for feedback from the forum first. Is this something that sounds interesting?