thermometers?

A commercial $75 solution is the HSM100 - Z-Wave Multi-Sensor which incorporates motion, illumination (light), and temperature sensors in one battery-operated, wireless module.

One can hope that SmartHome comes out with an upgrade to their 2420M INSTEON wireless motion sensor to provide temperature, humidity and light sensing,.

I use a bunch of Oregon Scientific wireless temperature and temperature/ humidity sensors + an RFXCOM 433.92 MHz RF receiver + Heyu software

Is that the THGR268? Might be the way to go...

The THGR268 will work, up to 3 units. Beyond that you'll need to select a different model which transmits at different intervals. Otherwise there will be signal corruption when 2 units repeatedly transmit at the same time.

How many sensors do you expect to be using?

Oops, thought I saw that it transmitted on a value change... I'm looking at roughly half a dozen.

At the moment, putting a thermistor on an XBee module is looking like my best option...

You could add THGR800 for up to 3 more or RTGR328N for up to 5 more or THGR810 for up to 10 more.

Thanks -- that's very helpful! But they don't seem to have anything that looks like a permanent installation...

I'm not sure what you mean by "permanent installation".

Are you perhaps thinking of AC powered sensors? If so there are other options supported by Heyu, e.g., RFXSensor

Smarthome's TempLinc 1625

I'm thinking in terms of an in-wall installation -- the best of all possible worlds would be if I could replace an existing junction box with a 2-gang, put the sensor in the new part, and power it off the AC.

I don't know of any such device. In any event although you might put a power supply module inside the box (assuming it meets code to do so), the temperature sensing element at least would have to be on the outside, open to the ambient air and probably somewhat remote so it's not influenced by the heat from the power supply. And you'd want the sensing element to be around 5 feet off the floor, not down at the level of most residential AC receptacles.

Have you looked into using Insteon thermostats , not for control but just for their remote thermometer function? You'd need to provide power equivalent to that available from normal thermostat wiring, which I think may be only a very small transformer.

One thing about in-wall is making sure you get a real reading. It needs to have proper air flow. The wall itself could be conducting heat/cold from another spot (the room on the other side of the wall, for example) or a close duct.

You'll notice on a thermostat it is mounted off the wall with lots of vents.

Right. Another thing to avoid if possible is mounting on an outside wall. The house insulation may be good but it's never perfect.

Do you mean the Venstar thermostats? Those are looking like the best products I've come across -- a small transformer should indeed supply power. These are looking like $160 a pop, however..

Lots of good points there, thanks

That's what I was thinking of. Pricey, yes, but you have some very specific requirements.

You might try contacting Smarthome to see if they have any less expensive recommendations. A lot of electronic thermostats seem to have the capability for remote temperature sensors and these could perhaps be used stand-alone.