This USB key can display how much space you've eaten up, using either a pie chart or digits. The screen also has an 11-character readout to help you remember what you stored. It's not an LCD, but a "Bi-stable Cholesteric" Display, which doesn't need power to maintain its image. Comes in capacities of 1 and 2GB.
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If johnb was here he'd probably post the same product twice, too.