Look for "i2s" modules. E.g. there's one for ~20EUR that adds a stereo ADC/DAC (e.g. also usable for the raspberry pi). It has a "i2s" interface which is the canonical way to interface with audio ADCs/DACs. This can easily be connected to any FPGA.

http://mbed.org/cookbook/RS-Audio-Codec

http://en.wikipedia.org/wiki/I%C2%B2S

http://blog.koalo.de/2013/05/i2s-support-for-raspberry-pi.ht...