Why do you need that accuracy?
Maxim (aka Dallas Semiconductor) carries single chip silicon-based temperature sensors accurate to 0.5C:
The DS600 is the only analog output device they have with that accuracy:
**broken link removed**
THe rest are digital interface such as the DS620 or DS7505:
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Needless to say, you could do the same thing with an RTD (with a much greater stability and accuracy over a much larger temperature range) at greatly increased cost, complexity, and hard to find parts.