This nifty little USB dongle adds mono audio input and stereo output through USB (1.0). It's a cheap and cheerful solution for audio input to your Raspberry Pi.
After testing a wide range of USB audio dongles, this was the winner through being simple, low on noise and artifacts, and free from pointless buttons, bells, and whistles. The ferrite bead on the cable is a nice little extra.
In Raspbian, this device should show up in the audio control panel automagically (go to the Raspberry Pi menu, then Preferences, then Audio Device Settings, and select USB PnP Sound Device).
We recommend providing a good signal to the input, as it provides no gain/boost for passive mics, but we do also have a USB microphone if you want simpler audio capture.
Once you're up and running, record audio input on your Pi, in the terminal, by typing:
arecord -D plughw:1 -f cd /tmp/recording.wav