I want a small, battery-operated gadget that communicates with a server via either 802.11 or Bluetooth (more likely, since it's much cheaper) that's capable of measuring the ambient temperature in the immediate area and sending that data to the server when queried.

Would probably need some form of single-wire temperature monitor (SparkFun Electronics seems to have these for cheap), a Bluetooth transciever, an a PIC for command, control, and comms.