National Instruments makes several products for digital and analog sensing. In fact, looking over their product line, they got this: NI USB-TC01. You buy that and a simple J-type thermocouple (it even looks like they have package deals on their site) and you'll get a highly accurate and reliable temperature reading wherever you place it. National Instruments hardware also uses their NIDAQmx driver package which has full native .NET assemblies for programming.

I use them all the time for doing industrial hardware automation. You don't need any additional software to program for them, just the drivers that come with the unit.