I have been experimenting with the WM8731 ADC/DAC chip (datasheet) and the raspberry pi using i2s and the aSOC drivers.
I chose this CODEC because it already had an aSOC driver written, and Koalo had already written the other driver file required which was based on his experience with the Mikroe audio CODEC proto board. The WM8731 happens to be a Wolfson chip and I have had good experience in the past with another Wolfson DAC – the WM8740 which I used in my DIY USB DAC.
This particular CODEC has both stereo headphone and line level outputs, a line level input plus a separate simple mic input with integrated mic bias. At this stage I am using it with a simple crystal at 12.288MHz. So a decent chip to play around with, and hopefully not much fuss setting it up.