Casio CZ-1000 - A light-weight, all-digital synthesizer which is exceptionally tedious to program. It has two particularly nice features: detunable oscillators and a ring modulator.
UPDATE (17-06-12): I'm passing this on to a friend who'll hopefully get more use out of it. I haven't used it on a single recording to date! I'm afraid I found it as inspiring as making music with a calculator.
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