M-Audio MobilePre USB

Product page at M-Audio: http://www.m-audio.com/products/en_ca/MobilePreUSB.html

2 x 2 16-bit/48kHz analog I/O

2 microphone inputs (XLR balanced) with 48v phantom power

stereo microphone input (1/8”)

2 high-impedance instrument/line inputs (balanced/unbalanced 1/4” TRS)

2 mono line outputs (1/4” @ -10dBV)

stereo line output (1/8”)

stereo headphone output with level control knob

gain control knob for each input channel (+40 dB max)

zero-latency hardware direct monitoring (mono/stereo) with software level control

USB-powered

As of April 2011, it can be purchased on Amazon for ~ $100 USD

There are no additional drivers required.

All features work in Linux.

Personal experience (forum user nealfunkbass): I have owned a MobilePre for several years, and it has worked out-of-the box on every Linux distribution I have tried (Ubuntu, Fedora, Arch, etc).