You can find a short list of some available cards here
Personally I like programming in C++ and use either Jackd or ALSA.
For Jackd, there is an example audio processing client here
. All you have to do is change the TestJackClient::processAudio method to what you want it to do ... that should be enough for your to test it and if you like it you can make it more yours !
The procedure to test would be compile it, then start jackd then start the test jack client.
For ALSA, you could make your own plugin. For that I like to use this class here
. It is more involved, but once you have it compiling, you can install it in the ALSA plugins directory and run it with any ALSA program. Example command syntax using aplay is like so :
aplay -D yourplugin yourFile.wav
hope that helps.