Amazon offers the 2nd-generation Nest Learning Thermostat, model no. T200577, for $199 with free shipping. That's the lowest total price we could find by $31 (outside the offers below), although we saw it for $10 less in February. It improves on its predecessor with a slimmer profile and 1-piece construction. It "learns" how you set your home's temperature, downloads data, and can be controlled from your smartphone (via WiFi). Note that not all home HVACs are Nest-compatible; click here to see if it will work with yours.
A couple close prices: Best Buy and Crutchfield both offer it for $199.99 with free shipping.