M-Audio Transit $99
This very basic external USB has a digital toslink input and output, as well as 1/8" analog line inputs/outputs. The digital I/O pass 24bit/96mhz digital audio. The line output can also be used as a headphone out. This is favorite amongst audiophiles which retails for only $99.95.

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M-Audio Audiophile USB $249

A step above the transit, the Audiophile USB has similar features and quality but is more suited to recording. It boasts full size RCA jacks for Analog Line In/Out, RCA Digital SPDIF In/Out, Midi Ports, Volume control, headphone output with independent volume control. Could be the unit to get if you're looking to transcribe your vinyl to your computer. The Audiophile USB also adds an external power supply, separate from your computers' noisy power supply.

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ESI Waveterminal U24 $299

Another small, portable external 24/96 USB sound card with all the features you need to get going: Digital and Analog I/O, Headphone output, internal digital mixer, sample rate converter, SPDIF or Optical digital connections, etc.

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